• acknowledged error-free, non-duplicated transfer of user data,
• data fragmentation to conform to discovered Path Maximum Transmission Unit (PMTU) size,
• sequenced delivery of user messages within multiple streams, with an option for order-of-arrival delivery of individual user messages,
• optional bundling of multiple user messages into a single SCTP packet, and
• network-level fault tolerance through supporting of multi-homing at either or both ends of an association.

• TCP provides both reliable data transfer and strict order-of-transmission delivery of data. Some applications need reliable transfer without sequence maintenance, while others would be satisfied with partial ordering of the data. In both of these cases, the head-of-line blocking offered by TCP causes unnecessary delay.
• The stream-oriented nature of TCP is often an inconvenience. Applications add their own record marking to delineate their messages and make explicit use of the push facility to ensure that a complete message is transferred in a reasonable time.
• The limited scope of TCP sockets complicates the task of providing highly available data transfer capability using multi-homed hosts.
• TCP is relatively vulnerable to denial-of-service attacks, such as SYN attacks.

Active Destination Transport Address:

A transport address on a peer endpoint that a transmitting endpoint considersavailable for receiving user messages.

Association Maximum DATA Chunk Size (AMDCS):

The smallest Path Maximum DATA Chunk Size (PMDCS) of all destinationaddresses.

Bundling of Chunks:

An optional multiplexing operation, whereby more than one chunk canbe carried in the same SCTP packet.

Bundling of User Messages:

An optional multiplexing operation, whereby more than one user message canbe carried in the same SCTP packet. Each user message occupies its own DATA chunk.

Chunk:

A unit of information within an SCTP packet, consisting of a chunk headerand chunk-specific content.

Congestion Window (cwnd):

An SCTP variable that limits outstanding data, in number of bytes,that a sender can send to a particular destination transport address beforereceiving an acknowledgement.

Control Chunk:

A chunk not being used for transmitting user data, i.e., every chunk thatis not a DATA chunk.

Cumulative TSN Ack Point:

The Transmission Sequence Number (TSN) of the last DATA chunk acknowledged viathe Cumulative TSN Ack field of a SACK chunk.

Flightsize:

The number of bytes of outstanding data to a particular destination transportaddress at any given time.

Idle Destination Address:

An address that has not had user messages sent to it within some lengthof time, normally the 'HB.interval' or greater.

Inactive Destination Transport Address:

An address that is considered inactive due to errors and unavailable totransport user messages.

Message (or User Message):

Data submitted to SCTP by the Upper-Layer Protocol (ULP).

Network Byte Order:

Most significant byte first, a.k.a., big endian.

Ordered Message:

A user message that is delivered in order with respect to all previous usermessages sent within the stream on which the message was sent.

Outstanding Data (or Data Outstanding or Data In Flight):

The total size of the DATA chunks associated with outstanding TSNs.A retransmitted DATA chunk is counted once in outstanding data.A DATA chunk that is classified as lost but that has not yet beenretransmitted is not in outstanding data.

Outstanding TSN (at an SCTP Endpoint):

A TSN (and the associated DATA chunk) that has been sent by the endpointbut for which it has not yet received an acknowledgement.

"Out of the Blue" (OOTB) Packet:

A correctly formed packet, for which the receiver cannot identify theassociation it belongs to. See Section 8.4.

Path:

The route taken by the SCTP packets sent by one SCTP endpoint to a specificdestination transport address of its peer SCTP endpoint.Sending to different destination transport addresses does not necessarilyguarantee getting separate paths.Within this specification, a path is identified by the destination transportaddress, since the routing is assumed to be stable.This includes, in particular, the source address being selected when sendingpackets to the destination address.

Path Maximum DATA Chunk Size (PMDCS):

The maximum size (including the DATA chunk header) of a DATA chunk that fitsinto an SCTP packet not exceeding the PMTU of a particular destination address.

Path Maximum Transmission Unit (PMTU):

The maximum size (including the SCTP common header and all chunks includingtheir paddings) of an SCTP packet that can be sent to a particulardestination address without using IP-level fragmentation.

Primary Path:

The destination and source address that will be put intoa packet outbound to the peer endpoint by default.The definition includes the source address since an implementation MAY wishto specify both destination and source address to better control the returnpath taken by reply chunks and on which interface the packet is transmittedwhen the data sender is multi-homed.

Receiver Window (rwnd):

An SCTP variable a data sender uses to store the most recently calculatedreceiver window of its peer, in number of bytes.This gives the sender an indication of the space available in the receiver'sinbound buffer.

SCTP Association:

A protocol relationship between SCTP endpoints, composed of the two SCTPendpoints and protocol state information, including Verification Tags and thecurrently active set of Transmission Sequence Numbers (TSNs), etc.An association can be uniquely identified by the transport addresses used by theendpoints in the association.Two SCTP endpoints MUST NOT have more than one SCTP association betweenthem at any given time.

SCTP Endpoint:

The logical sender/receiver of SCTP packets.On a multi-homed host, an SCTP endpoint is represented to its peers asa combination of a set of eligible destination transport addressesto which SCTP packets can be sent and a set of eligible sourcetransport addresses from which SCTP packets can be received.All transport addresses used by an SCTP endpoint MUST use the sameport number but can use multiple IP addresses.A transport address used by an SCTP endpoint MUST NOT be used by another SCTPendpoint.In other words, a transport address is unique to an SCTP endpoint.

SCTP Packet (or Packet):

The unit of data delivery across the interface between SCTP and theconnectionless packet network (e.g., IP).An SCTP packet includes the common SCTP header, possible SCTP control chunks,and user data encapsulated within SCTP DATA chunks.

SCTP User Application (or SCTP User):

The logical higher-layer application entity that uses the services of SCTP,also called the Upper-Layer Protocol (ULP).

Slow-Start Threshold (ssthresh):

An SCTP variable.This is the threshold that the endpoint will use to determine whether toperform slow-start or congestion avoidance on a particular destinationtransport address. Ssthresh is in number of bytes.

State Cookie:

A container of all information needed to establish an association.

Stream:

A unidirectional logical channel established from one to another associated SCTP endpoint, within which all user messages are delivered in sequence, except for those submitted to the unordered delivery service.

Note: The relationship between stream numbers in opposite directions is strictly a matter of how the applications use them. It is the responsibility of the SCTP user to create and manage these correlations if they are so desired.

Stream Sequence Number:

A 16-bit sequence number used internally by SCTP to ensure sequenced deliveryof the user messages within a given stream.One Stream Sequence Number is attached to each ordered user message.

Tie-Tags:

Two 32-bit random numbers that together make a 64-bit nonce.These tags are used within a State Cookie and TCB so that a newly restartingassociation can be linked to the original association within the endpointthat did not restart and yet not reveal the true Verification Tags of anexisting association.

Transmission Control Block (TCB):

An internal data structure created by an SCTP endpoint for each of itsexisting SCTP associations to other SCTP endpoints.TCB contains all the status and operational information for the endpointto maintain and manage the corresponding association.

Transmission Sequence Number (TSN):

A 32-bit sequence number used internally by SCTP.One TSN is attached to each chunk containing user data to permit thereceiving SCTP endpoint to acknowledge its receipt and detect duplicatedeliveries.

Transport Address:

A transport address is typically defined by a network-layer address,a transport-layer protocol, and a transport-layer port number.In the case of SCTP running over IP, a transport address is defined bythe combination of an IP address and an SCTP port number (where SCTP is thetransport protocol).

Unordered Message:

Unordered messages are "unordered" with respect to any other message;this includes both other unordered messages as well as other ordered messages.An unordered message might be delivered prior to or later than ordered messagessent on the same stream.

User Message:

The unit of data delivery across the interface between SCTP and its user.

Verification Tag:

A 32-bit unsigned integer that is randomly generated.The Verification Tag provides a key that allows a receiver to verify that theSCTP packet belongs to the current association and is not an old or stalepacket from a previous association.

MAC

Message Authentication Code [RFC 2104]

RTO

Retransmission Timeout

RTT

Round-Trip Time

RTTVAR

Round-Trip Time Variation

SCTP

Stream Control Transmission Protocol

SRTT

Smoothed RTT

TCB

Transmission Control Block

TLV

Type-Length-Value coding format

TSN

Transmission Sequence Number

ULP

Upper-Layer Protocol

• Update references.
• Improve the language related to requirements levels.
• Allow the ASSOCIATE primitive to take multiple remote addresses; also refer to the socket API specification.
• Refer to the Packetization Layer Path MTU Discovery (PLPMTUD) specification for path MTU discovery.
• Move the description of ICMP handling from the Appendix to the main text.
• Remove the Appendix describing Explicit Congestion Notification (ECN) handling from the document.
• Describe the packet size handling more precisely by introducing PMTU, PMDCS, and AMDCS.
• Add the definition of control chunk.
• Improve the description of the handling of INIT and INIT ACK chunks with invalid mandatory parameters.
• Allow using L > 1 for Appropriate Byte Counting (ABC) during slow start.
• Explicitly describe the reinitialization of the congestion controller on route changes.
• Improve the terminology to make it clear that this specification does not describe a full mesh architecture.
• Improve the description of sequence number generation (Transmission Sequence Number and Stream Sequence Number).
• Improve the description of reneging.
• Don't require the change of the Cumulative TSN Ack anymore for increasing the congestion window. This improves the consistency with the handling in congestion avoidance.
• Improve the description of the State Cookie.
• Fix the API for retrieving messages in case of association failures.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Source Port Number       |    Destination Port Number    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Verification Tag                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Checksum                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Source Port Number: 16 bits (unsigned integer)

This is the SCTP sender's port number.It can be used by the receiver in combination with the source IP address,the SCTP Destination Port Number, and possibly the destination IP address toidentify the association to which this packet belongs.The Source Port Number 0 MUST NOT be used.

Destination Port Number: 16 bits (unsigned integer)

This is the SCTP port number to which this packet is destined.The receiving host will use this port number to de-multiplex theSCTP packet to the correct receiving endpoint/application.The Destination Port Number 0 MUST NOT be used.

Verification Tag: 32 bits (unsigned integer)

The receiver of an SCTP packet uses the Verification Tag to validate the sender of this packet. On transmit, the value of the Verification Tag MUST be set to the value of the Initiate Tag received from the peer endpoint during the association initialization, with the following exceptions:

• A packet containing an INIT chunk MUST have a zero Verification Tag.
• A packet containing a SHUTDOWN COMPLETE chunk with the T bit set MUST have the Verification Tag copied from the packet with the SHUTDOWN ACK chunk.
• A packet containing an ABORT chunk MAY have the Verification Tag copied from the packet that caused the ABORT chunk to be sent. For details, see Sections [8.4] and [8.5].

Checksum: 32 bits (unsigned integer)

This field contains the checksum of the SCTP packet.Its calculation is discussed inSection 6.8.SCTP uses the CRC32c algorithm as described in Appendix A forcalculating the checksum.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Chunk Type   |  Chunk Flags  |         Chunk Length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                          Chunk Value                          /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Type: 8 bits (unsigned integer)

This field identifies the type of information contained in the Chunk Value field. It takes a value from 0 to 254. The value of 255 is reserved for future use as an extension field.

The values of Chunk Types defined in this document are as follows:

ID Value	Chunk Type
0	Payload Data (DATA)
1	Initiation (INIT)
2	Initiation Acknowledgement (INIT ACK)
3	Selective Acknowledgement (SACK)
4	Heartbeat Request (HEARTBEAT)
5	Heartbeat Acknowledgement (HEARTBEAT ACK)
6	Abort (ABORT)
7	Shutdown (SHUTDOWN)
8	Shutdown Acknowledgement (SHUTDOWN ACK)
9	Operation Error (ERROR)
10	State Cookie (COOKIE ECHO)
11	Cookie Acknowledgement (COOKIE ACK)
12	Reserved for Explicit Congestion Notification Echo (ECNE)
13	Reserved for Congestion Window Reduced (CWR)
14	Shutdown Complete (SHUTDOWN COMPLETE)
15 to 62	Unassigned
63	Reserved for IETF-defined Chunk Extensions
64 to 126	Unassigned
127	Reserved for IETF-defined Chunk Extensions
128 to 190	Unassigned
191	Reserved for IETF-defined Chunk Extensions
192 to 254	Unassigned
255	Reserved for IETF-defined Chunk Extensions

Table 1: Chunk Types

Note: The ECNE and CWR chunk types are reserved for future use of Explicit Congestion Notification (ECN).

Chunk Types are encoded such that the highest-order 2 bits specify the action that is taken if the processing endpoint does not recognize the Chunk Type.

00	Stop processing this SCTP packet and discard the unrecognized chunk and all further chunks.
01	Stop processing this SCTP packet, discard the unrecognized chunk and all further chunks, and report the unrecognized chunk in an ERROR chunk using the 'Unrecognized Chunk Type' error cause.
10	Skip this chunk and continue processing.
11	Skip this chunk and continue processing, but report it in an ERROR chunk using the 'Unrecognized Chunk Type' error cause.

Table 2: Processing of Unknown Chunks

Chunk Flags: 8 bits

The usage of these bits depends on the Chunk Type, as given by the Chunk Type field. Unless otherwise specified, they are set to 0 on transmit and are ignored on receipt.

Chunk Length: 16 bits (unsigned integer)

This value represents the size of the chunk in bytes, including the Chunk Type, Chunk Flags, Chunk Length, and Chunk Value fields. Therefore, if the Chunk Value field is zero-length, the Length field will be set to 4. The Chunk Length field does not count any chunk padding. However, it does include any padding of variable-length parameters other than the last parameter in the chunk.

Note: A robust implementation is expected to accept the chunk whether or not the final padding has been included in the Chunk Length.

Chunk Value: variable length

The Chunk Value field contains the actual information to be transferred in the chunk. The usage and format of this field is dependent on the Chunk Type.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Parameter Type         |       Parameter Length        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                        Parameter Value                        /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Parameter Type: 16 bits (unsigned integer)

The Type field is a 16-bit identifier of the type of parameter. It takes a value of 0 to 65534.

The value of 65535 is reserved for IETF-defined extensions. Values other than those defined in specific SCTP chunk descriptions are reserved for use by IETF.

Parameter Length: 16 bits (unsigned integer)

The Parameter Length field contains the size of the parameter inbytes, including the Parameter Type, Parameter Length, and Parameter Valuefields. Thus, a parameter with a zero-length Parameter Value field would have aParameter Length field of 4.The Parameter Length does not include any padding bytes.

Parameter Value: variable length

The Parameter Value field contains the actual information to be transferred in the parameter.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 0    |  Res  |I|U|B|E|            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              TSN                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Stream Identifier S      |   Stream Sequence Number n    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Payload Protocol Identifier                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                 User Data (seq n of Stream S)                 /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Res: 4 bits

All set to 0 on transmit and ignored on receipt.

I bit: 1 bit

The (I)mmediate bit MAY be set by the sender whenever the sender of a DATAchunk can benefit from the corresponding SACK chunk being sent back without delay.See Section 4 of RFC 7053 for a discussion of the benefits.

U bit: 1 bit

The (U)nordered bit, if set to 1, indicates that this is an unordered DATA chunk, and there is no Stream Sequence Number assigned to this DATA chunk. Therefore, the receiver MUST ignore the Stream Sequence Number field.

After reassembly (if necessary), unordered DATA chunks MUST be dispatched to the upper layer by the receiver without any attempt to reorder.

If an unordered user message is fragmented, each fragment of the message MUST have its U bit set to 1.

B bit: 1 bit

The (B)eginning fragment bit, if set, indicates the first fragment of auser message.

E bit: 1 bit

The (E)nding fragment bit, if set, indicates the last fragment ofa user message.

Length: 16 bits (unsigned integer)

This field indicates the length of the DATA chunk in bytes from the beginning of the type field to the end of the User Data field excluding any padding. A DATA chunk with one byte of user data will have the Length field set to 17 (indicating 17 bytes).

A DATA chunk with a User Data field of length L will have the Length field set to (16 + L) (indicating 16 + L bytes) where L MUST be greater than 0.

TSN: 32 bits (unsigned integer)

This value represents the TSN for this DATA chunk.The valid range of TSN is from 0 to 4294967295 (2³² - 1).TSN wraps back to 0 after reaching 4294967295.

Stream Identifier S: 16 bits (unsigned integer)

Identifies the stream to which the following user data belongs.

Stream Sequence Number n: 16 bits (unsigned integer)

This value represents the Stream Sequence Number of the following user data within the stream S. Valid range is 0 to 65535.

When a user message is fragmented by SCTP for transport, the same Stream Sequence Number MUST be carried in each of the fragments of the message.

Payload Protocol Identifier: 32 bits (unsigned integer)

This value represents an application (or upper layer) specified protocol identifier. This value is passed to SCTP by its upper layer and sent to its peer. This identifier is not used by SCTP but can be used by certain network entities, as well as by the peer application, to identify the type of information being carried in this DATA chunk. This field MUST be sent even in fragmented DATA chunks (to make sure it is available for agents in the middle of the network). Note that this field is not touched by an SCTP implementation; the upper layer is responsible for the host to network byte order conversion of this field.

The value 0 indicates that no application identifier is specified by the upper layer for this payload data.

User Data: variable length

This is the payload user data.The implementation MUST pad the end of the data to a 4-byte boundary withall zero bytes.Any padding MUST NOT be included in the Length field.A sender MUST never add more than 3 bytes of padding.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 1    |  Chunk Flags  |      Chunk Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Initiate Tag                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Advertised Receiver Window Credit (a_rwnd)           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Number of Outbound Streams   |   Number of Inbound Streams   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Initial TSN                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/              Optional/Variable-Length Parameters              /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Initiate Tag: 32 bits (unsigned integer)

The receiver of the INIT chunk (the responding end) records the value of the Initiate Tag parameter. This value MUST be placed into the Verification Tag field of every SCTP packet that the receiver of the INIT chunk transmits within this association.

The Initiate Tag is allowed to have any value except 0. See Section 5.3.1 for more on the selection of the tag value.

If the value of the Initiate Tag in a received INIT chunk is found to be 0, the receiver MUST silently discard the packet.

Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned integer)

This value represents the dedicated buffer space, in number of bytes, the sender of the INIT chunk has reserved in association with this window.

The Advertised Receiver Window Credit MUST NOT be smaller than 1500.

A receiver of an INIT chunk with the a_rwnd value set to a value smaller than 1500 MUST discard the packet, SHOULD send a packet in response containing an ABORT chunk and using the Initiate Tag as the Verification Tag, and MUST NOT change the state of any existing association.

During the life of the association, this buffer space SHOULD NOT be reduced (i.e., dedicated buffers ought not to be taken away from this association); however, an endpoint MAY change the value of a_rwnd it sends in SACK chunks.

Number of Outbound Streams (OS): 16 bits (unsigned integer)

Defines the number of outbound streams the sender of this INIT chunk wishes to create in this association. The value of 0 MUST NOT be used.

A receiver of an INIT chunk with the OS value set to 0 MUST discard the packet, SHOULD send a packet in response containing an ABORT chunk and using the Initiate Tag as the Verification Tag, and MUST NOT change the state of any existing association.

Number of Inbound Streams (MIS): 16 bits (unsigned integer)

Defines the maximum number of streams the sender of this INIT chunk allows the peer end to create in this association. The value 0 MUST NOT be used.

Note: There is no negotiation of the actual number of streams; instead, the two endpoints will use the min(requested, offered). See Section 5.1.1 for details.

A receiver of an INIT chunk with the MIS value set to 0 MUST discard the packet, SHOULD send a packet in response containing an ABORT chunk and using the Initiate Tag as the Verification Tag, and MUST NOT change the state of any existing association.

Initial TSN (I-TSN): 32 bits (unsigned integer)

Defines the TSN that the sender of the INIT chunk will use initially.The valid range is from 0 to 4294967295 and the Initial TSN SHOULD be set to arandom value in that range.The methods described in [RFC 4086] can be used for theInitial TSN randomization.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type = 5            |          Length = 8           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         IPv4 Address                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IPv4 Address: 32 bits (unsigned integer)

Contains an IPv4 address of the sending endpoint.It is binary encoded.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type = 6            |          Length = 20          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                         IPv6 Address                          |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IPv6 Address: 128 bits (unsigned integer)

Contains an IPv6 [RFC 8200] address of the sending endpoint. It is binary encoded.

A sender MUST NOT use an IPv4-mapped IPv6 address [RFC 4291] but SHOULD instead use an IPv4 Address parameter for an IPv4 address.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type = 9            |          Length = 8           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Suggested Cookie Life-Span Increment (msec.)          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Suggested Cookie Life-Span Increment: 32 bits (unsigned integer)

This parameter indicates to the receiver how much increment in milliseconds the sender wishes the receiver to add to its default cookie life span.

This optional parameter MAY be added to the INIT chunk by the sender when it reattempts establishing an association with a peer to which its previous attempt of establishing the association failed due to a stale cookie operation error. The receiver MAY choose to ignore the suggested cookie life span increase for its own security reasons.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type = 11           |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                           Host Name                           /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Host Name: variable length

This field contains a host name in "host name syntax" per Section 2.1 of RFC 1123. The method for resolving the host name is out of scope of SCTP.

At least one null terminator is included in the Host Name string and MUST be included in the length.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type = 12           |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Address Type #1        |        Address Type #2        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            ......                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+

Address Type: 16 bits (unsigned integer)

This is filled with the type value of the corresponding addressTLV (e.g., 5 for indicating IPv4, and 6 for indicating IPv6).The value indicating the Host Name Address parameter MUST NOT be usedwhen sending this parameter and MUST be ignored when receiving thisparameter.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 2    |  Chunk Flags  |         Chunk Length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Initiate Tag                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               Advertised Receiver Window Credit               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Number of Outbound Streams   |   Number of Inbound Streams   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Initial TSN                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/              Optional/Variable-Length Parameters              /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Initiate Tag: 32 bits (unsigned integer)

The receiver of the INIT ACK chunk records the value of the Initiate Tag parameter. This value MUST be placed into the Verification Tag field of every SCTP packet that the receiver of the INIT ACK chunk transmits within this association.

The Initiate Tag MUST NOT take the value 0. See Section 5.3.1 for more on the selection of the Initiate Tag value.

If an endpoint in the COOKIE-WAIT state receives an INIT ACK chunk with the Initiate Tag set to 0, it MUST destroy the TCB and SHOULD send an ABORT chunk with the T bit set. If such an INIT ACK chunk is received in any state other than CLOSED or COOKIE-WAIT, it SHOULD be discarded silently (see Section 5.2.3).

Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned integer)

This value represents the dedicated buffer space, in number of bytes, the sender of the INIT ACK chunk has reserved in association with this window.

The Advertised Receiver Window Credit MUST NOT be smaller than 1500.

A receiver of an INIT ACK chunk with the a_rwnd value set to a value smaller than 1500 MUST discard the packet, SHOULD send a packet in response containing an ABORT chunk and using the Initiate Tag as the Verification Tag, and MUST NOT change the state of any existing association.

During the life of the association, this buffer space SHOULD NOT be reduced (i.e., dedicated buffers ought not to be taken away from this association); however, an endpoint MAY change the value of a_rwnd it sends in SACK chunks.

Number of Outbound Streams (OS): 16 bits (unsigned integer)

Defines the number of outbound streams the sender of this INIT ACK chunk wishes to create in this association. The value of 0 MUST NOT be used, and the value MUST NOT be greater than the MIS value sent in the INIT chunk.

If an endpoint in the COOKIE-WAIT state receives an INIT ACK chunk with the OS value set to 0, it MUST destroy the TCB and SHOULD send an ABORT chunk. If such an INIT ACK chunk is received in any state other than CLOSED or COOKIE-WAIT, it SHOULD be discarded silently (see Section 5.2.3).

Number of Inbound Streams (MIS): 16 bits (unsigned integer)

Defines the maximum number of streams the sender of this INIT ACK chunk allows the peer end to create in this association. The value 0 MUST NOT be used.

Note: There is no negotiation of the actual number of streams, but instead the two endpoints will use the min(requested, offered). See Section 5.1.1 for details.

If an endpoint in the COOKIE-WAIT state receives an INIT ACK chunk with the MIS value set to 0, it MUST destroy the TCB and SHOULD send an ABORT chunk. If such an INIT ACK chunk is received in any state other than CLOSED or COOKIE-WAIT, it SHOULD be discarded silently (see Section 5.2.3).

Initial TSN (I-TSN): 32 bits (unsigned integer)

Defines the TSN that the sender of the INIT ACK chunk will use initially.The valid range is from 0 to 4294967295 and the Initial TSN SHOULD be set to arandom value in that range.The methods described in [RFC 4086] can be used for theInitial TSN randomization.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type = 7            |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                            Cookie                             /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Cookie: variable length

This parameter value MUST contain all the necessary state and parameterinformation required for the sender of this INIT ACK chunk to create theassociation, along with a Message Authentication Code (MAC).See Section 5.1.3 for details onState Cookie definition.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type = 8            |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                    Unrecognized Parameter                     /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Unrecognized Parameter: variable length

The Parameter Value field will contain an unrecognized parameter copied fromthe INIT chunk complete with Parameter Type, Length, and Value fields.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 3    |  Chunk Flags  |         Chunk Length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Cumulative TSN Ack                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Advertised Receiver Window Credit (a_rwnd)           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Gap Ack Blocks = N  |  Number of Duplicate TSNs = M |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Gap Ack Block #1 Start     |     Gap Ack Block #1 End      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                              ...                              \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Gap Ack Block #N Start     |     Gap Ack Block #N End      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Duplicate TSN 1                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                              ...                              \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Duplicate TSN M                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

All set to 0 on transmit and ignored on receipt.

Cumulative TSN Ack: 32 bits (unsigned integer)

The largest TSN, such that all TSNs smaller than or equal to it have beenreceived and the next one has not been received.In the case where no DATA chunk has been received, this value is set to thepeer's Initial TSN minus one.

Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned integer)

This field indicates the updated receive buffer space in bytes of the senderof this SACK chunk; see Section 6.2.1 for details.

Number of Gap Ack Blocks: 16 bits (unsigned integer)

Indicates the number of Gap Ack Blocks included in this SACK chunk.

Number of Duplicate TSNs: 16 bit

This field contains the number of duplicate TSNs the endpoint has received.Each duplicate TSN is listed following the Gap Ack Block list.

Gap Ack Blocks:

These fields contain the Gap Ack Blocks.They are repeated for each Gap Ack Block up to the number of Gap Ack Blocksdefined in the Number of Gap Ack Blocks field.All DATA chunks with TSNs greater than or equal to (Cumulative TSN Ack +Gap Ack Block Start) and less than or equal to (Cumulative TSN Ack +Gap Ack Block End) of each Gap Ack Block are assumed to have been receivedcorrectly.

Gap Ack Block Start: 16 bits (unsigned integer)

Indicates the Start offset TSN for this Gap Ack Block.To calculate the actual TSN number, the Cumulative TSN Ack is added tothis offset number.This calculated TSN identifies the lowest TSN in this Gap Ack Block that hasbeen received.

Gap Ack Block End: 16 bits (unsigned integer)

Indicates the End offset TSN for this Gap Ack Block. To calculate the actual TSN number, the Cumulative TSN Ack is added to this offset number. This calculated TSN identifies the highest TSN in this Gap Ack Block that has been received.

For example, assume that the receiver has the following DATA chunks newly arrived at the time when it decides to send a Selective ACK:

------------
| TSN = 17 |
------------
|          | <- still missing
------------
| TSN = 15 |
------------
| TSN = 14 |
------------
|          | <- still missing
------------
| TSN = 12 |
------------
| TSN = 11 |
------------
| TSN = 10 |
------------

Then, the parameter part of the SACK chunk MUST be constructed as follows (assuming the new a_rwnd is set to 4660 by the sender):

+-------------------+-------------------+
|        Cumulative TSN Ack = 12        |
+-------------------+-------------------+
|             a_rwnd = 4660             |
+-------------------+-------------------+
| num of block = 2  |  num of dup = 0   |
+-------------------+-------------------+
|block #1 start = 2 | block #1 end = 3  |
+-------------------+-------------------+
|block #2 start = 5 | block #2 end = 5  |
+-------------------+-------------------+

Duplicate TSN: 32 bits (unsigned integer)

Indicates the number of times a TSN was received in duplicate since the last SACK chunk was sent. Every time a receiver gets a duplicate TSN (before sending the SACK chunk), it adds it to the list of duplicates. The duplicate count is reinitialized to zero after sending each SACK chunk.

For example, if a receiver were to get the TSN 19 three times, it would list 19 twice in the outbound SACK chunk. After sending the SACK chunk, if it received yet one more TSN 19, it would list 19 as a duplicate once in the next outgoing SACK chunk.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 4    |  Chunk Flags  |       Heartbeat Length        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/          Heartbeat Information TLV (Variable-Length)          /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Set to 0 on transmit and ignored on receipt.

Heartbeat Length: 16 bits (unsigned integer)

Set to the size of the chunk in bytes, including the chunk header and theHeartbeat Information field.

Heartbeat Information: variable length

Defined as a variable-length parameter using the format described in Section 3.2.1, that is:

Variable Parameters	Status	Type Value
Heartbeat Info	Mandatory	1

Table 9: Variable-Length Parameters of HEARTBEAT Chunks

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Heartbeat Info Type = 1    |        HB Info Length         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                Sender-Specific Heartbeat Info                 /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Sender-Specific Heartbeat Info field SHOULD include information about the sender's current time when this HEARTBEAT chunk is sent and the destination transport address to which this HEARTBEAT chunk is sent (see Section 8.3). This information is simply reflected back by the receiver in the HEARTBEAT ACK chunk (see Section 3.3.6). Note also that the HEARTBEAT chunk is both for reachability checking and for path verification (see Section 5.4). When a HEARTBEAT chunk is being used for path verification purposes, it MUST include a random nonce of length 64 bits or longer ([RFC 4086] provides some information on randomness guidelines).

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 5    |  Chunk Flags  |     Heartbeat Ack Length      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/          Heartbeat Information TLV (Variable-Length)          /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Set to 0 on transmit and ignored on receipt.

Heartbeat Ack Length: 16 bits (unsigned integer)

Set to the size of the chunk in bytes, including the chunk header and theHeartbeat Information field.

Heartbeat Information: variable length

This field MUST contain the Heartbeat Info parameter (as defined in Section 3.3.5) of the Heartbeat Request to which this Heartbeat Acknowledgement is responding.

Variable Parameters	Status	Type Value
Heartbeat Info	Mandatory	1

Table 10: Variable-Length Parameters of HEARTBEAT ACK Chunks

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 6    |  Reserved   |T|            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                   zero or more Error Causes                   /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Reserved: 7 bits

Set to 0 on transmit and ignored on receipt.

T bit: 1 bit

The T bit is set to 0 if the sender filled in the Verification Tagexpected by the peer.If the Verification Tag is reflected, the T bit MUST be set to 1.Reflecting means that the sent Verification Tag is the same as the received one.

Length: 16 bits (unsigned integer)

Set to the size of the chunk in bytes, including the chunk header and all theError Cause fields present.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 7    |  Chunk Flags  |          Length = 8           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Cumulative TSN Ack                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Set to 0 on transmit and ignored on receipt.

Length: 16 bits (unsigned integer)

Indicates the length of the parameter. Set to 8.

Cumulative TSN Ack: 32 bits (unsigned integer)

The largest TSN, such that all TSNs smaller than or equal to it have beenreceived and the next one has not been received.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 8    |  Chunk Flags  |          Length = 4           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Set to 0 on transmit and ignored on receipt.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 9    |  Chunk Flags  |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                   one or more Error Causes                    /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Set to 0 on transmit and ignored on receipt.

Length: 16 bits (unsigned integer)

Set to the size of the chunk in bytes, including the chunk header and all theError Cause fields present.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Cause Code           |         Cause Length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                  Cause-Specific Information                   /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Cause Code: 16 bits (unsigned integer)

Defines the type of error conditions being reported.

Value	Cause Code
1	Invalid Stream Identifier
2	Missing Mandatory Parameter
3	Stale Cookie
4	Out of Resource
5	Unresolvable Address
6	Unrecognized Chunk Type
7	Invalid Mandatory Parameter
8	Unrecognized Parameters
9	No User Data
10	Cookie Received While Shutting Down
11	Restart of an Association with New Addresses
12	User-Initiated Abort
13	Protocol Violation

Table 11: Cause Code

Cause Length: 16 bits (unsigned integer)

Set to the size of the parameter in bytes, including the Cause Code,Cause Length, and Cause-Specific Information fields.

Cause-Specific Information: variable length

This field carries the details of the error condition.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Cause Code = 1         |       Cause Length = 8        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Stream Identifier       |          (Reserved)           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Stream Identifier: 16 bits (unsigned integer)

Contains the Stream Identifier of the DATA chunk received in error.

Reserved: 16 bits

This field is reserved.It is set to all 0's on transmit and ignored on receipt.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Cause Code = 2         |   Cause Length = 8 + N * 2    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 Number of missing params = N                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Missing Param Type #1     |     Missing Param Type #2     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Missing Param Type #N-1    |     Missing Param Type #N     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Number of Missing params: 32 bits (unsigned integer)

This field contains the number of parameters contained in the Cause-SpecificInformation field.

Missing Param Type: 16 bits (unsigned integer)

Each field will contain the missing mandatory parameter number.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Cause Code = 3         |       Cause Length = 8        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 Measure of Staleness (usec.)                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Measure of Staleness: 32 bits (unsigned integer)

This field contains the difference, rounded up in microseconds, between the current time and the time the State Cookie expired.

The sender of this error cause MAY choose to report how long past expiration the State Cookie is by including a non-zero value in the Measure of Staleness field. If the sender does not wish to provide the Measure of Staleness, it SHOULD set this field to the value of zero.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Cause Code = 5         |         Cause Length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                     Unresolvable Address                      /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Unresolvable Address: variable length

The Unresolvable Address field contains the complete Type, Length, and Valueof the address parameter (or Host Name parameter) that contains theunresolvable address or host name.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Cause Code = 6         |         Cause Length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                      Unrecognized Chunk                       /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Unrecognized Chunk: variable length

The Unrecognized Chunk field contains the unrecognized chunk from theSCTP packet complete with Chunk Type, Chunk Flags, and Chunk Length.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Cause Code = 8         |         Cause Length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                    Unrecognized Parameters                    /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Unrecognized Parameters: variable length

The Unrecognized Parameters field contains the unrecognized parameters copiedfrom the INIT ACK chunk complete with TLV.This error cause is normally contained in an ERROR chunk bundled withthe COOKIE ECHO chunk when responding to the INIT ACK chunk, when thesender of the COOKIE ECHO chunk wishes to report unrecognized parameters.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Cause Code = 9         |       Cause Length = 8        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              TSN                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

TSN: 32 bits (unsigned integer)

This parameter contains the TSN of the DATA chunk received with no UserData field.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 10   |  Chunk Flags  |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                            Cookie                             /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Set to 0 on transmit and ignored on receipt.

Length: 16 bits (unsigned integer)

Set to the size of the chunk in bytes, including the 4 bytes of thechunk header and the size of the cookie.

Cookie: variable size

This field MUST contain the exact cookie received in the State Cookie parameter from the previous INIT ACK chunk.

An implementation SHOULD make the cookie as small as possible to ensure interoperability.

Note: A Cookie Echo does not contain a State Cookie parameter; instead, the data within the State Cookie's Parameter Value becomes the data within the Cookie Echo's Chunk Value. This allows an implementation to change only the first 2 bytes of the State Cookie parameter to become a COOKIE ECHO chunk.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 11   |  Chunk Flags  |          Length = 4           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Set to 0 on transmit and ignored on receipt.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type = 14   |  Reserved   |T|          Length = 4           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Chunk Flags: 8 bits

Reserved: 7 bits

Set to 0 on transmit and ignored on receipt.

T bit: 1 bit

The T bit is set to 0 if the sender filled in the Verification Tagexpected by the peer.If the Verification Tag is reflected, the T bit MUST be set to 1.Reflecting means that the sent Verification Tag is the same as thereceived one.

• SCTP user primitive calls, e.g., [ASSOCIATE], [SHUTDOWN], or [ABORT],
• reception of INIT, COOKIE ECHO, ABORT, SHUTDOWN, etc., and control chunks, or
• some timeout events.

                        -----          -------- (from any state)
                      /       \      /receive ABORT      [ABORT]
        receive INIT |         |    |--------------  or ----------
---------------------|         v    v    delete TCB     send ABORT
generate State Cookie \    +---------+                  delete TCB
        send INIT ACK   ---|  CLOSED |
                           +---------+
                             /      \
                            /        \  [ASSOCIATE]
                           |          |-----------------
                           |          | create TCB
                           |          | send INIT
          receive valid    |          | start T1-init timer
          COOKIE  ECHO     |          v
      (1) -----------------|    +-----------+
          create TCB       |    |COOKIE-WAIT| (2)
          send COOKIE ACK  |    +-----------+
                           |          |
                           |          | receive INIT ACK
                           |          |-------------------
                           |          | send COOKIE ECHO
                           |          | stop T1-init timer
                           |          | start T1-cookie timer
                           |          v
                           |   +-------------+
                           |   |COOKIE-ECHOED| (3)
                           |   +-------------+
                           |          |
                           |          | receive COOKIE ACK
                           |          |-------------------
                           |          | stop T1-cookie timer
                           v          v
                         +---------------+
                         |  ESTABLISHED  |
                         +---------------+
                                 |
                                 |
                        /--------+--------\
    [SHUTDOWN]         /                   \
    -------------------|                   |
    check outstanding  |                   |
    DATA chunks        |                   |
                       v                   |
              +----------------+           |
              |SHUTDOWN-PENDING|           | receive SHUTDOWN
              +----------------+           |------------------
                                           | check outstanding
                       |                   | DATA chunks
No more outstanding    |                   |
-----------------------|                   |
send SHUTDOWN          |                   |
start T2-shutdown timer|                   |
                       v                   v
                +-------------+   +-----------------+
            (4) |SHUTDOWN-SENT|   |SHUTDOWN-RECEIVED| (5,6)
                +-------------+   +-----------------+
                       |  \                |
receive SHUTDOWN ACK   |   \               |
-----------------------|    \              |
stop T2-shutdown timer |     \             |
send SHUTDOWN COMPLETE |      \            |
delete TCB             |       \           |
                       |        \          | No more outstanding
                       |         \         |--------------------
                       |          \        | send SHUTDOWN ACK
receive SHUTDOWN      -|-          \       | start T2-shutdown timer
--------------------/  | \----------\      |
send SHUTDOWN ACK      |             \     |
start T2-shutdown timer|              \    |
                       |               \   |
                       |                |  |
                       |                v  v
                       |          +-----------------+
                       |          |SHUTDOWN-ACK-SENT| (7)
                       |          +-----------------+
                       |                   | (A)
                       |                   |receive SHUTDOWN COMPLETE
                       |                   |-------------------------
                       |                   | stop T2-shutdown timer
                       |                   | delete TCB
                       |                   |
                       |                   | (B)
                       |                   | receive SHUTDOWN ACK
                       |                   |-----------------------
                       |                   | stop T2-shutdown timer
                       |                   | send SHUTDOWN COMPLETE
                       |                   | delete TCB
                       |                   |
                       \    +---------+    /
                        \-->| CLOSED  |<--/
                            +---------+

1)

If the State Cookie in the received COOKIE ECHO chunk is invalid (i.e., failed to pass the integrity check), the receiver MUST silently discard the packet. Or, if the received State Cookie is expired (see Section 5.1.5), the receiver MUST send back an ERROR chunk. In either case, the receiver stays in the CLOSED state.

2)

If the T1-init timer expires, the endpoint MUST retransmit the INIT chunk and restart the T1-init timer. The endpoint stays in the COOKIE-WAIT state. This MUST be repeated up to 'Max.Init.Retransmits' times. After that, the endpoint MUST abort the initialization process and report the error to the SCTP user.

3)

If the T1-cookie timer expires, the endpoint MUST retransmit COOKIE ECHO chunk and restart the T1-cookie timer. The endpoint stays in the COOKIE-ECHOED state. This MUST be repeated up to 'Max.Init.Retransmits' times. After that, the endpoint MUST abort the initialization process and report the error to the SCTP user.

4)

In the SHUTDOWN-SENT state, the endpoint MUST acknowledge any received DATA chunks without delay.

5)

In the SHUTDOWN-RECEIVED state, the endpoint MUST NOT accept any new send requests from its SCTP user.

6)

In the SHUTDOWN-RECEIVED state, the endpoint MUST transmit or retransmit data and leave this state when all data in queue is transmitted.

7)

In the SHUTDOWN-ACK-SENT state, the endpoint MUST NOT accept any new send requests from its SCTP user.

A)

"A" first builds a TCB and sends an INIT chunk to "Z". In the INIT chunk, "A" MUST provide its Verification Tag (Tag_A) in the Initiate Tag field. Tag_A SHOULD be a random number in the range of 1 to 4294967295 (see Section 5.3.1 for Tag value selection). After sending the INIT chunk, "A" starts the T1-init timer and enters the COOKIE-WAIT state.

B)

"Z" responds immediately with an INIT ACK chunk. The destination IP address of the INIT ACK chunk MUST be set to the source IP address of the INIT chunk to which this INIT ACK chunk is responding. In the response, besides filling in other parameters, "Z" MUST set the Verification Tag field to Tag_A and also provide its own Verification Tag (Tag_Z) in the Initiate Tag field. Moreover, "Z" MUST generate and send along with the INIT ACK chunk a State Cookie. See Section 5.1.3 for State Cookie generation. After sending an INIT ACK chunk with the State Cookie parameter, "Z" MUST NOT allocate any resources or keep any states for the new association. Otherwise, "Z" will be vulnerable to resource attacks.

C)

Upon reception of the INIT ACK chunk from "Z", "A" stops the T1-init timer and leaves the COOKIE-WAIT state. "A" then sends the State Cookie received in the INIT ACK chunk in a COOKIE ECHO chunk, starts the T1-cookie timer, and enters the COOKIE-ECHOED state. The COOKIE ECHO chunk MAY be bundled with any pending outbound DATA chunks, but it MUST be the first chunk in the packet and, until the COOKIE ACK chunk is returned, the sender MUST NOT send any other packets to the peer.

D)

Upon reception of the COOKIE ECHO chunk, endpoint "Z" replies with a COOKIE ACK chunk after building a TCB and moving to the ESTABLISHED state. A COOKIE ACK chunk MAY be bundled with any pending DATA chunks (and/or SACK chunks), but the COOKIE ACK chunk MUST be the first chunk in the packet. Implementation Note: An implementation can choose to send the COMMUNICATION UP notification to the SCTP user upon reception of a valid COOKIE ECHO chunk.

E)

Upon reception of the COOKIE ACK chunk, endpoint "A" moves from the COOKIE-ECHOED state to the ESTABLISHED state, stopping the T1-cookie timer. It can also notify its ULP about the successful establishment of the association with a COMMUNICATION UP notification (see Section 11).

A)

If there are no address parameters present in the received INIT or INIT ACK chunk, the endpoint MUST take the source IP address from which the chunk arrives and record it, in combination with the SCTP Source Port Number, as the only destination transport address for this peer.

B)

If there is a Host Name Address parameter present in the received INIT or INIT ACK chunk, the endpoint MUST immediately send an ABORT chunk and MAY include an "Unresolvable Address" error cause to its peer. The ABORT chunk SHOULD be sent to the source IP address from which the last peer packet was received.

C)

If there are only IPv4/IPv6 addresses present in the received INIT or INIT ACK chunk, the receiver MUST derive and record all the transport addresses from the received chunk AND the source IP address that sent the INIT or INIT ACK chunk. The transport addresses are derived by the combination of SCTP Source Port Number (from the common header) and the IP Address parameter(s) carried in the INIT or INIT ACK chunk and the source IP address of the IP datagram. The receiver SHOULD use only these transport addresses as destination transport addresses when sending subsequent packets to its peer.

D)

An INIT or INIT ACK chunk MUST be treated as belonging to an already established association (or one in the process of being established) if the use of any of the valid address parameters contained within the chunk would identify an existing TCB.

1)

Compute a MAC using the information carried in the State Cookie and the secret key. The timestamp in the State Cookie MAY be used to determine which secret key to use. If secrets are kept only for a limited amount of time and the secret key to use is not available anymore, the packet containing the COOKIE ECHO chunk MUST be silently discarded. [RFC 2104] can be used as a guideline for generating the MAC.

2)

Authenticate the State Cookie as one that it previously generated by comparing the computed MAC against the one carried in the State Cookie. If this comparison fails, the SCTP packet, including the COOKIE ECHO chunk and any DATA chunks, MUST be silently discarded.

3)

Compare the port numbers and the Verification Tag contained within the COOKIE ECHO chunk to the actual port numbers and the Verification Tag within the SCTP common header of the received packet. If these values do not match, the packet MUST be silently discarded.

4)

Compare the creation timestamp in the State Cookie to the current local time. If the elapsed time is longer than the lifespan carried in the State Cookie, then the packet, including the COOKIE ECHO chunk and any attached DATA chunks, SHOULD be discarded, and the endpoint MUST transmit an ERROR chunk with a "Stale Cookie" error cause to the peer endpoint.

5)

If the State Cookie is valid, create an association to the sender of the COOKIE ECHO chunk with the information in the State Cookie carried in the COOKIE ECHO chunk and enter the ESTABLISHED state.

6)

Send a COOKIE ACK chunk to the peer acknowledging receipt of the COOKIE ECHO chunk. The COOKIE ACK chunk MAY be bundled with an outbound DATA chunk or SACK chunk; however, the COOKIE ACK chunk MUST be the first chunk in the SCTP packet.

7)

Immediately acknowledge any DATA chunk bundled with the COOKIE ECHO chunk with a SACK chunk (subsequent DATA chunk acknowledgement SHOULD follow the rules defined in Section 6.2). As mentioned in step 6, if the SACK chunk is bundled with the COOKIE ACK chunk, the COOKIE ACK chunk MUST appear first in the SCTP packet.

A)

the peer has crashed without being detected, restarted itself, and sent a new INIT chunk trying to restore the association,

B)

both sides are trying to initialize the association at about the same time,

C)

the chunk is from a stale packet that was used to establish the present association or a past association that is no longer in existence,

D)

the chunk is a false packet generated by an attacker, or

E)

the peer never received the COOKIE ACK chunk and is retransmitting its COOKIE ECHO chunk.

1)

The packet containing the INIT ACK chunk MUST only be sent to an address passed by the upper layer in the request to initialize the association.

2)

The packet containing the INIT ACK chunk MUST only be sent to an address reported in the incoming INIT chunk.

3)

The packet containing the INIT ACK chunk SHOULD be sent to the source address of the received packet containing the INIT chunk.

1)

Compute a MAC as described in step 1 of Section 5.1.5.

2)

Authenticate the State Cookie as described in step 2 of Section 5.1.5 (this is case C or D above).

3)

Compare the timestamp in the State Cookie to the current time. If the State Cookie is older than the lifespan carried in the State Cookie and the Verification Tags contained in the State Cookie do not match the current association's Verification Tags, the packet, including the COOKIE ECHO chunk and any DATA chunks, SHOULD be discarded. The endpoint also MUST transmit an ERROR chunk with a "Stale Cookie" error cause to the peer endpoint (this is case C or D in Section 5.2). If both Verification Tags in the State Cookie match the Verification Tags of the current association, consider the State Cookie valid (this is case E in Section 5.2), even if the lifespan is exceeded.

4)

If the State Cookie proves to be valid, unpack the TCB into a temporary TCB.

5)

Refer to Table 12 to determine the correct action to be taken.

X -

Tag does not match the existing TCB.

M -

Tag matches the existing TCB.

0 -

Tag unknown (Peer's Tag not known yet / No Tie-Tag in cookie).

A -

All cases, i.e., M, X, or 0.

A)

In this case, the peer might have restarted. When the endpoint recognizes this potential 'restart', the existing session is treated the same as if it received an ABORT chunk followed by a new COOKIE ECHO chunk with the following exceptions:

• Any SCTP DATA chunks MAY be retained (this is an implementation-specific option).
• A RESTART notification SHOULD be sent to the ULP instead of a COMMUNICATION LOST notification.

All the congestion control parameters (e.g., cwnd, ssthresh) related to this peer MUST be reset to their initial values (see Section 6.2.1). After this, the endpoint enters the ESTABLISHED state. If the endpoint is in the SHUTDOWN-ACK-SENT state and recognizes that the peer has restarted (Action A), it MUST NOT set up a new association but instead resend the SHUTDOWN ACK chunk and send an ERROR chunk with a "Cookie Received While Shutting Down" error cause to its peer.

B)

In this case, both sides might be attempting to start an association at about the same time, but the peer endpoint sent its INIT chunk after responding to the local endpoint's INIT chunk. Thus, it might have picked a new Verification Tag, not being aware of the previous tag it had sent this endpoint. The endpoint SHOULD stay in or enter the ESTABLISHED state, but it MUST update its peer's Verification Tag from the State Cookie, stop any T1-init or T1-cookie timers that might be running, and send a COOKIE ACK chunk.

C)

In this case, the local endpoint's cookie has arrived late. Before it arrived, the local endpoint sent an INIT chunk and received an INIT ACK chunk and finally sent a COOKIE ECHO chunk with the peer's same tag but a new tag of its own. The cookie SHOULD be silently discarded. The endpoint SHOULD NOT change states and SHOULD leave any timers running.

D)

When both local and remote tags match, the endpoint SHOULD enter the ESTABLISHED state if it is in the COOKIE-ECHOED state. It SHOULD stop any T1-cookie timer that is running and send a COOKIE ACK chunk.

A)

The association failed to completely set up before the State Cookie issued by the sender was processed.

B)

An old State Cookie was processed after setup completed.

C)

An old State Cookie is received from someone that the receiver is not interested in having an association with and the ABORT chunk was lost.

1)

Send a new INIT chunk to the endpoint to generate a new State Cookie and reattempt the setup procedure.

2)

Discard the TCB and report to the upper layer the inability to set up the association.

3)

Send a new INIT chunk to the endpoint, adding a Cookie Preservative parameter requesting an extension to the life time of the State Cookie. When calculating the time extension, an implementation SHOULD use the RTT information measured based on the previous COOKIE ECHO/ERROR chunk exchange and SHOULD add no more than 1 second beyond the measured RTT, due to long State Cookie life times making the endpoint more subject to a replay attack.

1)

Any addresses passed to the sender of the INIT chunk by its upper layer in the request to initialize an association are automatically considered to be CONFIRMED.

2)

For the receiver of the COOKIE ECHO chunk, the only CONFIRMED address is the address to which the packet containing the INIT ACK chunk was sent.

3)

All other addresses not covered by rules 1 and 2 are considered UNCONFIRMED and are subject to probing for verification.

• A HEARTBEAT chunk including a nonce MAY be sent to an UNCONFIRMED address.
• A HEARTBEAT ACK chunk MAY be sent to an UNCONFIRMED address.
• A COOKIE ACK chunk MAY be sent to an UNCONFIRMED address, but it MUST be bundled with a HEARTBEAT chunk including a nonce. An implementation that does not support bundling MUST NOT send a COOKIE ACK chunk to an UNCONFIRMED address.
• A COOKIE ECHO chunk MAY be sent to an UNCONFIRMED address, but it MUST be bundled with a HEARTBEAT chunk including a nonce, and the size of the SCTP packet MUST NOT exceed the PMTU. If the implementation does not support bundling or if the bundled COOKIE ECHO chunk plus HEARTBEAT chunk (including nonce) would result in an SCTP packet larger than the PMTU, then the implementation MUST NOT send a COOKIE ECHO chunk to an UNCONFIRMED address.

           +-------------------------+
           |      User Messages      |
           +-------------------------+
 SCTP user        ^  |
==================|==|=======================================
                  |  v (1)
       +------------------+    +---------------------+
       | SCTP DATA Chunks |    | SCTP Control Chunks |
       +------------------+    +---------------------+
                  ^  |             ^  |
                  |  v (2)         |  v (2)
               +--------------------------+
               |       SCTP packets       |
               +--------------------------+
 SCTP                      ^  |
===========================|==|===========================
                           |  v
       Connectionless Packet Transfer Service (e.g., IP)

1)

When converting user messages into DATA chunks, an endpoint MUST fragment large user messages into multiple DATA chunks. The size of each DATA chunk SHOULD be smaller than or equal to the Association Maximum DATA Chunk Size (AMDCS). The data receiver will normally reassemble the fragmented message from DATA chunks before delivery to the user (see Section 6.9 for details).

2)

Multiple DATA and control chunks MAY be bundled by the sender into a single SCTP packet for transmission, as long as the final size of the SCTP packet does not exceed the current PMTU. The receiver will unbundle the packet back into the original chunks. Control chunks MUST come before DATA chunks in the packet.

A)

At any given time, the data sender MUST NOT transmit new data to any destination transport address if its peer's rwnd indicates that the peer has no buffer space (i.e., rwnd is smaller than the size of the next DATA chunk; see Section 6.2.1), except for zero window probes. A zero window probe is a DATA chunk sent when the receiver has no buffer space. This rule allows the sender to probe for a change in rwnd that the sender missed due to the SACK chunks having been lost in transit from the data receiver to the data sender. A zero window probe MUST only be sent when the cwnd allows (see rule B below). A zero window probe SHOULD only be sent when all outstanding DATA chunks have been cumulatively acknowledged and no DATA chunks are in flight. Senders MUST support zero window probing. If the sender continues to receive SACK chunks from the peer while doing zero window probing, the unacknowledged window probes SHOULD NOT increment the error counter for the association or any destination transport address. This is because the receiver could keep its window closed for an indefinite time. Section 6.2 describes the receiver behavior when it advertises a zero window. The sender SHOULD send the first zero window probe after 1 RTO when it detects that the receiver has closed its window and SHOULD increase the probe interval exponentially afterwards. Also note that the cwnd SHOULD be adjusted according to Section 7.2.1. Zero window probing does not affect the calculation of cwnd. The sender MUST also have an algorithm for sending new DATA chunks to avoid silly window syndrome (SWS) as described in [RFC 1122]. The algorithm can be similar to the one described in Section 4.2.3.4 of RFC 1122.

B)

At any given time, the sender MUST NOT transmit new data to a given transport address if it has cwnd + (PMDCS - 1) or more bytes of data outstanding to that transport address. If data is available, the sender SHOULD exceed cwnd by up to (PMDCS - 1) bytes on a new data transmission if the flightsize does not currently reach cwnd. The breach of cwnd MUST constitute one packet only.

C)

When the time comes for the sender to transmit, before sending new DATA chunks, the sender MUST first transmit any DATA chunks that are marked for retransmission (limited by the current cwnd).

D)

When the time comes for the sender to transmit new DATA chunks, the protocol parameter 'Max.Burst' SHOULD be used to limit the number of packets sent. The limit MAY be applied by adjusting cwnd temporarily, as follows:

if ((flightsize + Max.Burst * PMDCS) < cwnd)
    cwnd = flightsize + Max.Burst * PMDCS

Or, it MAY be applied by strictly limiting the number of packets emitted by the output routine. When calculating the number of packets to transmit, and particularly when using the formula above, cwnd SHOULD NOT be changed permanently.

E)

Then, the sender can send as many new DATA chunks as rule A and rule B allow.

• The application requests that the I bit of the last DATA chunk of a user message be set when providing the user message to the SCTP implementation (see Section 11.1).
• The sender is in the SHUTDOWN-PENDING state.
• The sending of a DATA chunk fills the congestion or receiver window.

A)

At initialization of the association, the endpoint tells the peer how much receive buffer space it has allocated to the association in the INIT or INIT ACK chunk. The endpoint sets a_rwnd to this value.

B)

As DATA chunks are received and buffered, decrement a_rwnd by the number of bytes received and buffered. This is, in effect, closing rwnd at the data sender and restricting the amount of data it can transmit.

C)

As DATA chunks are delivered to the ULP and released from the receive buffers, increment a_rwnd by the number of bytes delivered to the upper layer. This is, in effect, opening up rwnd on the data sender and allowing it to send more data. The data receiver SHOULD NOT increment a_rwnd unless it has released bytes from its receive buffer. For example, if the receiver is holding fragmented DATA chunks in a reassembly queue, it SHOULD NOT increment a_rwnd.

D)

When sending a SACK chunk, the data receiver SHOULD place the current value of a_rwnd into the a_rwnd field. The data receiver SHOULD take into account that the data sender will not retransmit DATA chunks that are acked via the Cumulative TSN Ack (i.e., will drop from its retransmit queue).

Endpoint A                                      Endpoint Z

{App sends 3 messages; strm 0}
DATA [TSN=7,Strm=0,Seq=3] ------------> (ack delayed)
(Start T3-rtx timer)

DATA [TSN=8,Strm=0,Seq=4] ------------> (send ack)
                              /------- SACK [TSN Ack=8,block=0]
(cancel T3-rtx timer)  <-----/

DATA [TSN=9,Strm=0,Seq=5] ------------> (ack delayed)
(Start T3-rtx timer)
                                       ...
                                       {App sends 1 message; strm 1}
                                       (bundle SACK with DATA)
                                /----- SACK [TSN Ack=9,block=0] \
                               /         DATA [TSN=6,Strm=1,Seq=2]
(cancel T3-rtx timer)  <------/        (Start T3-rtx timer)

(ack delayed)
(send ack)
SACK [TSN Ack=6,block=0] -------------> (cancel T3-rtx timer)

A)

At the establishment of the association, the endpoint initializes the rwnd to the Advertised Receiver Window Credit (a_rwnd) the peer specified in the INIT or INIT ACK chunk.

B)

Any time a DATA chunk is transmitted (or retransmitted) to a peer, the endpoint subtracts the data size of the chunk from the rwnd of that peer.

C)

Any time a DATA chunk is marked for retransmission, either via T3-rtx timer expiration (Section 6.3.3) or via Fast Retransmit (Section 7.2.4), add the data size of those chunks to the rwnd.

D)

Any time a SACK chunk arrives, the endpoint performs the following:

i)

If Cumulative TSN Ack is less than the Cumulative TSN Ack Point, then drop the SACK chunk. Since Cumulative TSN Ack is monotonically increasing, a SACK chunk whose Cumulative TSN Ack is less than the Cumulative TSN Ack Point indicates an out-of-order SACK chunk.

ii)

Set rwnd equal to the newly received a_rwnd minus the number of bytes still outstanding after processing the Cumulative TSN Ack and the Gap Ack Blocks.

iii)

If the SACK chunk is missing a TSN that was previously acknowledged via a Gap Ack Block (e.g., the data receiver reneged on the data), then consider the corresponding DATA that might be possibly missing: Count one miss indication towards Fast Retransmit as described in Section 7.2.4, and if no retransmit timer is running for the destination address to which the DATA chunk was originally transmitted, then T3-rtx is started for that destination address.

iv)

If the Cumulative TSN Ack matches or exceeds the Fast Recovery exit point (Section 7.2.4), Fast Recovery is exited.

C1)

Until an RTT measurement has been made for a packet sent to the given destination transport address, set RTO to the protocol parameter 'RTO.Initial'.

C2)

When the first RTT measurement R is made, perform:

SRTT = R
RTTVAR = R/2
RTO = SRTT + 4 * RTTVAR

C3)

When a new RTT measurement R' is made, perform:

RTTVAR = (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'|
SRTT = (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'

Note: The value of SRTT used in the update to RTTVAR is its value before updating SRTT itself using the second assignment. After the computation, update:

RTO = SRTT + 4 * RTTVAR

C4)

When data is in flight and when allowed by rule C5 below, a new RTT measurement MUST be made each round trip. Furthermore, new RTT measurements SHOULD be made no more than once per round trip for a given destination transport address. There are two reasons for this recommendation: First, it appears that measuring more frequently often does not in practice yield any significant benefit [ALLMAN99]; second, if measurements are made more often, then the values of 'RTO.Alpha' and 'RTO.Beta' in rule C3 above SHOULD be adjusted so that SRTT and RTTVAR still adjust to changes at roughly the same rate (in terms of how many round trips it takes them to reflect new values) as they would if making only one measurement per round trip and using 'RTO.Alpha' and 'RTO.Beta' as given in rule C3. However, the exact nature of these adjustments remains a research issue.

C5)

Karn's algorithm: RTT measurements MUST NOT be made using chunks that were retransmitted (and thus for which it is ambiguous whether the reply was for the first instance of the chunk or for a later instance). RTT measurements SHOULD only be made using a DATA chunk with TSN r if no DATA chunk with TSN less than or equal to r was retransmitted since the DATA chunk with TSN r was sent first.

C6)

Whenever RTO is computed, if it is less than 'RTO.Min' seconds, then it is rounded up to 'RTO.Min' seconds. The reason for this rule is that RTOs that do not have a high minimum value are susceptible to unnecessary timeouts [ALLMAN99].

C7)

A maximum value MAY be placed on RTO, provided it is at least 'RTO.Max' seconds.

G1)

Whenever RTTVAR is computed, if RTTVAR == 0, then adjust RTTVAR = G.

R1)

Every time a DATA chunk is sent to any address (including a retransmission), if the T3-rtx timer of that address is not running, start it running so that it will expire after the RTO of that address. The RTO used here is that obtained after any doubling due to previous T3-rtx timer expirations on the corresponding destination address as discussed in rule E2 below.

R2)

Whenever all outstanding data sent to an address have been acknowledged, turn off the T3-rtx timer of that address.

R3)

Whenever a SACK chunk is received that acknowledges the DATA chunk with the earliest outstanding TSN for that address, restart the T3-rtx timer for that address with its current RTO (if there is still outstanding data on that address).

R4)

Whenever a SACK chunk is received missing a TSN that was previously acknowledged via a Gap Ack Block, start the T3-rtx for the destination address to which the DATA chunk was originally transmitted if it is not already running.

Endpoint A                                         Endpoint Z
{App begins to send}
Data [TSN=7,Strm=0,Seq=3] ------------> (ack delayed)
(Start T3-rtx timer)
                                        {App sends 1 message; strm 1}
                                        (bundle ack with data)
DATA [TSN=8,Strm=0,Seq=4] ----\     /-- SACK [TSN Ack=7,Block=0]
                               \   /      DATA [TSN=6,Strm=1,Seq=2]
                                \ /     (Start T3-rtx timer)
                                 \
                                / \
(Restart T3-rtx timer)  <------/   \--> (ack delayed)
(ack delayed)
{send ack}
SACK [TSN Ack=6,Block=0] --------------> (Cancel T3-rtx timer)
                                        ..
                                        (send ack)
(Cancel T3-rtx timer)  <-------------- SACK [TSN Ack=8,Block=0]

E1)

For the destination address for which the timer expires, adjust its ssthresh with rules defined in Section 7.2.3 and set cwnd = PMDCS.

E2)

For the destination address for which the timer expires, set RTO = RTO * 2 ("back off the timer"). The maximum value discussed in rule C7 above ('RTO.Max') MAY be used to provide an upper bound to this doubling operation.

E3)

Determine how many of the earliest (i.e., lowest TSN) outstanding DATA chunks for the address for which the T3-rtx has expired will fit into a single SCTP packet, subject to the PMTU corresponding to the destination transport address to which the retransmission is being sent (this might be different from the address for which the timer expires; see Section 6.4). Call this value K. Bundle and retransmit those K DATA chunks in a single packet to the destination endpoint.

E4)

Start the retransmission timer T3-rtx on the destination address to which the retransmission is sent if rule R1 above indicates to do so. The RTO to be used for starting T3-rtx SHOULD be the one for the destination address to which the retransmission is sent, which, when the receiver is multi-homed, might be different from the destination address for which the timer expired (see Section 6.4 below).

F1)

Whenever an endpoint switches from the current destination transport address to a different one, the current retransmission timers are left running. As soon as the endpoint transmits a packet containing DATA chunk(s) to the new transport address, start the timer on that transport address, using the RTO value of the destination address to which the data is being sent, if rule R1 indicates to do so.

1)

fill in the proper Verification Tag in the SCTP common header and initialize the checksum field to 0,

2)

calculate the CRC32c checksum of the whole packet, including the SCTP common header and all the chunks (refer to Appendix A for details of the CRC32c algorithm), and

3)

put the resultant value into the checksum field in the common header and leave the rest of the bits unchanged.

1)

Store the received CRC32c checksum value aside.

2)

Replace the 32 bits of the checksum field in the received SCTP packet with 0 and calculate a CRC32c checksum value of the whole received packet.

3)

Verify that the calculated CRC32c checksum is the same as the received CRC32c checksum. If it is not, the receiver MUST treat the packet as an invalid SCTP packet.

1)

The data sender MUST break the user message into a series of DATA chunks. The sender SHOULD choose a size of DATA chunks that is smaller than or equal to the AMDCS.

2)

The transmitter MUST then assign, in sequence, a separate TSN to each of the DATA chunks in the series. The transmitter assigns the same Stream Sequence Number to each of the DATA chunks. If the user indicates that the user message is to be delivered using unordered delivery, then the U flag of each DATA chunk of the user message MUST be set to 1.

3)

The transmitter MUST also set the B/E bits of the first DATA chunk in the series to 10, the B/E bits of the last DATA chunk in the series to 01, and the B/E bits of all other DATA chunks in the series to 00.

• The sender usually uses the same destination address until being instructed by the upper layer to do otherwise; however, SCTP MAY change to an alternate destination in the event an address is marked inactive (see Section 8.2). Also, SCTP MAY retransmit to a different transport address than the original transmission.
• The sender keeps a separate congestion control parameter set for each of the destination addresses it can send to (not each source-destination pair but for each destination). The parameters SHOULD decay if the address is not used for a long enough time period. [RFC 5681] specifies this period of time as a retransmission timeout.
• For each of the destination addresses, an endpoint does slow start upon the first transmission to that address.

• Receiver advertised window size (rwnd, in bytes), which is set by the receiver based on its available buffer space for incoming packets. Note: This variable is kept on the entire association.
• Congestion control window (cwnd, in bytes), which is adjusted by the sender based on observed network conditions. Note: This variable is maintained on a per-destination-address basis.
• Slow-start threshold (ssthresh, in bytes), which is used by the sender to distinguish slow-start and congestion avoidance phases. Note: This variable is maintained on a per-destination-address basis.

• The initial cwnd before data transmission MUST be set to min(4 * PMDCS, max(2 * PMDCS, 4404)) bytes if the peer address is an IPv4 address and to min(4 * PMDCS, max(2 * PMDCS, 4344)) bytes if the peer address is an IPv6 address.
• The initial cwnd after a retransmission timeout MUST be no more than PMDCS, and only one packet is allowed to be in flight until successful acknowledgement.
• The initial value of ssthresh SHOULD be arbitrarily high (e.g., the size of the largest-possible advertised window).
• Whenever cwnd is greater than zero, the endpoint is allowed to have cwnd bytes of data outstanding on that transport address. A limited overbooking as described in rule B in Section 6.1 SHOULD be supported.
• When cwnd is less than or equal to ssthresh, an SCTP endpoint MUST use the slow-start algorithm to increase cwnd only if the current congestion window is being fully utilized and the data sender is not in Fast Recovery. Only when these two conditions are met can the cwnd be increased; otherwise, the cwnd MUST NOT be increased. If these conditions are met, then cwnd MUST be increased by, at most, the lesser of
  1. the total size of the previously outstanding DATA chunk(s) acknowledged and
  2. L times the destination's PMDCS.
  The first upper bound protects against the ACK-Splitting attack outlined in [SAVAGE99]. The positive integer L SHOULD be 1 and MAY be larger than 1. See [RFC 3465] for details of choosing L. In instances where its peer endpoint is multi-homed, if an endpoint receives a SACK chunk that results in updating the cwnd, then it SHOULD update its cwnd (or cwnds) apportioned to the destination addresses to which it transmitted the acknowledged data.
• While the endpoint does not transmit data on a given transport address, the cwnd of the transport address SHOULD be adjusted to max(cwnd / 2, 4 * PMDCS) once per RTO. Before the first cwnd adjustment, the ssthresh of the transport address SHOULD be set to the cwnd.

• SCTP MAY increment cwnd by PMDCS.
• SCTP SHOULD increment cwnd by PMDCS once per RTT when the sender has cwnd or more bytes of data outstanding for the corresponding transport address.
• SCTP MUST NOT increment cwnd by more than PMDCS per RTT.

• partial_bytes_acked is initialized to 0.
• Whenever cwnd is greater than ssthresh, upon each SACK chunk arrival, increase partial_bytes_acked by the total number of bytes (including the chunk header and the padding) of all new DATA chunks acknowledged in that SACK chunk, including chunks acknowledged by the new Cumulative TSN Ack, by Gap Ack Blocks, and by the number of bytes of duplicated chunks reported in Duplicate TSNs.
• When (1) partial_bytes_acked is greater than cwnd and (2) before the arrival of the SACK chunk the sender had less than cwnd bytes of data outstanding (i.e., before the arrival of the SACK chunk, flightsize was less than cwnd), reset partial_bytes_acked to cwnd.
• When (1) partial_bytes_acked is equal to or greater than cwnd and (2) before the arrival of the SACK chunk the sender had cwnd or more bytes of data outstanding (i.e., before the arrival of the SACK chunk, flightsize was greater than or equal to cwnd), partial_bytes_acked is reset to (partial_bytes_acked - cwnd). Next, cwnd is increased by PMDCS.
• Same as in the slow start, when the sender does not transmit DATA chunks on a given transport address, the cwnd of the transport address SHOULD be adjusted to max(cwnd / 2, 4 * PMDCS) per RTO.
• When all of the data transmitted by the sender has been acknowledged by the receiver, partial_bytes_acked is initialized to 0.

1)

Mark the DATA chunk(s) with three miss indications for retransmission.

2)

If not in Fast Recovery, adjust the ssthresh and cwnd of the destination address(es) to which the missing DATA chunks were last sent, according to the formula described in Section 7.2.3.

3)

If not in Fast Recovery, determine how many of the earliest (i.e., lowest TSN) DATA chunks marked for retransmission will fit into a single packet, subject to constraint of the PMTU of the destination transport address to which the packet is being sent. Call this value K. Retransmit those K DATA chunks in a single packet. When a Fast Retransmit is being performed, the sender SHOULD ignore the value of cwnd and SHOULD NOT delay retransmission for this single packet.

4)

Restart the T3-rtx timer only if the last SACK chunk acknowledged the lowest outstanding TSN number sent to that address or the endpoint is retransmitting the first outstanding DATA chunk sent to that address.

5)

Mark the DATA chunk(s) as being fast retransmitted and thus ineligible for a subsequent Fast Retransmit. Those TSNs marked for retransmission due to the Fast-Retransmit algorithm that did not fit in the sent datagram carrying K other TSNs are also marked as ineligible for a subsequent Fast Retransmit. However, as they are marked for retransmission, they will be retransmitted later on as soon as cwnd allows.

6)

If not in Fast Recovery, enter Fast Recovery and mark the highest outstanding TSN as the Fast Recovery exit point. When a SACK chunk acknowledges all TSNs up to and including this exit point, Fast Recovery is exited. While in Fast Recovery, the ssthresh and cwnd SHOULD NOT change for any destinations due to a subsequent Fast Recovery event (i.e., one SHOULD NOT reduce the cwnd further due to a subsequent Fast Retransmit).

1)

SCTP associations can span multiple addresses. An endpoint MUST maintain separate PMTU estimates for each destination address of its peer.

2)

The sender SHOULD track an AMDCS that will be the smallest PMDCS discovered for all of the peer's destination addresses. When fragmenting messages into multiple parts, this AMDCS SHOULD be used to calculate the size of each DATA chunk. This will allow retransmissions to be seamlessly sent to an alternate address without encountering IP fragmentation.

A)

Disable heartbeat on a specific destination transport address of a given association,

B)

Change the 'HB.interval',

C)

Re-enable heartbeat on a specific destination transport address of a given association, and

D)

Request the sending of an on-demand HEARTBEAT chunk on a specific destination transport address of a given association.

1)

If the OOTB packet is to or from a non-unicast address, a receiver SHOULD silently discard the packet. Otherwise,

2)

If the OOTB packet contains an ABORT chunk, the receiver MUST silently discard the OOTB packet and take no further action. Otherwise,

3)

If the packet contains an INIT chunk with a Verification Tag set to 0, it SHOULD be processed as described in Section 5.1. If, for whatever reason, the INIT chunk cannot be processed normally and an ABORT chunk has to be sent in response, the Verification Tag of the packet containing the ABORT chunk MUST be the Initiate Tag of the received INIT chunk, and the T bit of the ABORT chunk has to be set to 0, indicating that the Verification Tag is not reflected. Otherwise,

4)

If the packet contains a COOKIE ECHO chunk as the first chunk, it MUST be processed as described in Section 5.1. Otherwise,

5)

If the packet contains a SHUTDOWN ACK chunk, the receiver SHOULD respond to the sender of the OOTB packet with a SHUTDOWN COMPLETE chunk. When sending the SHUTDOWN COMPLETE chunk, the receiver of the OOTB packet MUST fill in the Verification Tag field of the outbound packet with the Verification Tag received in the SHUTDOWN ACK chunk and set the T bit in the Chunk Flags to indicate that the Verification Tag is reflected. Otherwise,

6)

If the packet contains a SHUTDOWN COMPLETE chunk, the receiver SHOULD silently discard the packet and take no further action. Otherwise,

7)

If the packet contains an ERROR chunk with the "Stale Cookie" error cause or a COOKIE ACK chunk, the SCTP packet SHOULD be silently discarded. Otherwise,

8)

The receiver SHOULD respond to the sender of the OOTB packet with an ABORT chunk. When sending the ABORT chunk, the receiver of the OOTB packet MUST fill in the Verification Tag field of the outbound packet with the value found in the Verification Tag field of the OOTB packet and set the T bit in the Chunk Flags to indicate that the Verification Tag is reflected. After sending this ABORT chunk, the receiver of the OOTB packet MUST discard the OOTB packet and MUST NOT take any further action.

A) Rules for packets carrying an INIT chunk:

• The sender MUST set the Verification Tag of the packet to 0.
• When an endpoint receives an SCTP packet with the Verification Tag set to 0, it SHOULD verify that the packet contains only an INIT chunk. Otherwise, the receiver MUST silently discard the packet.

B) Rules for packets carrying an ABORT chunk:

• The endpoint MUST always fill in the Verification Tag field of the outbound packet with the destination endpoint's tag value if it is known.
• If the ABORT chunk is sent in response to an OOTB packet, the endpoint MUST follow the procedure described in Section 8.4.
• The receiver of an ABORT chunk MUST accept the packet if the Verification Tag field of the packet matches its own tag and the T bit is not set OR if it is set to its Peer's Tag and the T bit is set in the Chunk Flags. Otherwise, the receiver MUST silently discard the packet and take no further action.

C) Rules for packets carrying a SHUTDOWN COMPLETE chunk:

• When sending a SHUTDOWN COMPLETE chunk, if the receiver of the SHUTDOWN ACK chunk has a TCB, then the destination endpoint's tag MUST be used and the T bit MUST NOT be set. Only where no TCB exists SHOULD the sender use the Verification Tag from the SHUTDOWN ACK chunk and MUST set the T bit.
• The receiver of a SHUTDOWN COMPLETE chunk accepts the packet if the Verification Tag field of the packet matches its own tag and the T bit is not set OR if it is set to its Peer's Tag and the T bit is set in the Chunk Flags. Otherwise, the receiver MUST silently discard the packet and take no further action. An endpoint MUST ignore the SHUTDOWN COMPLETE chunk if it is not in the SHUTDOWN-ACK-SENT state.

D) Rules for packets carrying a COOKIE ECHO chunk:

• When sending a COOKIE ECHO chunk, the endpoint MUST use the value of the Initiate Tag received in the INIT ACK chunk.
• The receiver of a COOKIE ECHO chunk follows the procedures in Section 5.

E) Rules for packets carrying a SHUTDOWN ACK chunk:

• If the receiver is in COOKIE-ECHOED or COOKIE-WAIT state, the procedures in Section 8.4 SHOULD be followed; in other words, it is treated as an OOTB packet.

• enter the SHUTDOWN-RECEIVED state,
• stop accepting new data from its SCTP user, and
• verify, by checking the Cumulative TSN Ack field of the chunk, that all its outstanding DATA chunks have been received by the SHUTDOWN chunk sender.

ICMP1)

An implementation MAY ignore all ICMPv4 messages where the type field is not set to "Destination Unreachable".

ICMP2)

An implementation MAY ignore all ICMPv6 messages where the type field is not "Destination Unreachable", "Parameter Problem", or "Packet Too Big".

ICMP3)

An implementation SHOULD ignore any ICMP messages where the code indicates "Port Unreachable".

ICMP4)

An implementation MAY ignore all ICMPv6 messages of type "Parameter Problem" if the code is not "Unrecognized Next Header Type Encountered".

ICMP5)

An implementation MUST use the payload of the ICMP message (v4 or v6) to locate the association that sent the message to which ICMP is responding. If the association cannot be found, an implementation SHOULD ignore the ICMP message.

ICMP6)

An implementation MUST validate that the Verification Tag contained in the ICMP message matches the Verification Tag of the peer. If the Verification Tag is not 0 and does not match, discard the ICMP message. If it is 0 and the ICMP message contains enough bytes to verify that the chunk type is an INIT chunk and that the Initiate Tag matches the tag of the peer, continue with ICMP7. If the ICMP message is too short or the chunk type or the Initiate Tag does not match, silently discard the packet.

ICMP7)

If the ICMP message is either an ICMPv6 message of type "Packet Too Big" or an ICMPv4 message of type "Destination Unreachable" and code "Fragmentation Needed", an implementation SHOULD process this information as defined for PMTU discovery.

ICMP8)

If the ICMP code is "Unrecognized Next Header Type Encountered" or "Protocol Unreachable", an implementation MUST treat this message as an abort with the T bit set if it does not contain an INIT chunk. If it does contain an INIT chunk and the association is in the COOKIE-WAIT state, handle the ICMP message like an ABORT chunk.

ICMP9)

If the ICMP type is "Destination Unreachable", the implementation MAY move the destination to the unreachable state or, alternatively, increment the path error counter. SCTP MAY provide information to the upper layer indicating the reception of ICMP messages when reporting a network status change.

INITIALIZE ([local port],[local eligible address list])
-> local SCTP instance name

Mandatory attributes:

None.

Optional attributes:

local port:

SCTP port number, if ULP wants it to be specified.

local eligible address list:

an address list that the local SCTP endpoint binds.By default, if an address list is not included, all IP addresses assigned tothe host are used by the local endpoint.

ASSOCIATE(local SCTP instance name,
initial destination transport addr list, outbound stream count)
-> association id [,destination transport addr list]
[,outbound stream count]

Mandatory attributes:

local SCTP instance name:

obtained from the INITIALIZE operation.

initial destination transport addr list:

a non-empty list of transport addresses of the peer endpoint with whichthe association is to be established.

outbound stream count:

the number of outbound streams the ULP would like to open towards thispeer endpoint.

Optional attributes:

None.

SHUTDOWN(association id) -> result

Mandatory attributes:

association id:

local handle to the SCTP association.

Optional attributes:

None.

ABORT(association id [, Upper Layer Abort Reason]) -> result

Mandatory attributes:

association id:

local handle to the SCTP association.

Optional attributes:

Upper Layer Abort Reason:

reason of the abort to be passed to the peer.

SEND(association id, buffer address, byte count [,context]
[,stream id] [,life time] [,destination transport address]
[,unordered flag] [,no-bundle flag] [,payload protocol-id]
[,sack-immediately flag]) -> result

Mandatory attributes:

association id:

local handle to the SCTP association.

buffer address:

the location where the user message to be transmitted is stored.

byte count:

the size of the user data in number of bytes.

Optional attributes:

context:

optional information provided that will be carried in the SEND FAILUREnotification to the ULP if the transportation of this user message fails.

stream id:

indicates which stream to send the data on.If not specified, stream 0 will be used.

life time:

specifies the life time of the user data. The user data will not be sent by SCTP after the life time expires. This parameter can be used to avoid efforts to transmit stale user messages. SCTP notifies the ULP if the data cannot be initiated to transport (i.e., sent to the destination via SCTP's SEND primitive) within the life time variable. However, the user data will be transmitted if SCTP has attempted to transmit a chunk before the life time expired.

Implementation Note: In order to better support the data life time option, the transmitter can hold back the assigning of the TSN number to an outbound DATA chunk to the last moment. And, for implementation simplicity, once a TSN number has been assigned, the sender considers the send of this DATA chunk as committed, overriding any life time option attached to the DATA chunk.

destination transport address:

specified as one of the destination transport addresses of the peer endpointto which this packet is sent.Whenever possible, SCTP uses this destination transport address forsending the packets, instead of the current primary path.

unordered flag:

this flag, if present, indicates that the user would like the data deliveredin an unordered fashion to the peer (i.e., the U flag is set to 1 on all DATAchunks carrying this message).

no-bundle flag:

instructs SCTP not to delay the sending of DATA chunks for this user datajust to allow it to be bundled with other outbound DATA chunks.When faced with network congestion, SCTP might still bundle the data, even whenthis flag is present.

payload protocol-id:

a 32-bit unsigned integer that is to be passed to the peer, indicating the typeof payload protocol data being transmitted.Note that the upper layer is responsible for the host to network byte orderconversion of this field, which is passed by SCTP as 4 bytes of opaquedata.

sack-immediately flag:

set the I bit on the last DATA chunk used for the user message to betransmitted.

SETPRIMARY(association id, destination transport address,
[source transport address]) -> result

Mandatory attributes:

association id:

local handle to the SCTP association.

destination transport address:

specified as one of the transport addresses of the peer endpoint, which isused as the primary address for sending packets.This overrides the current primary address information maintained by thelocal SCTP endpoint.

Optional attributes:

source transport address:

optionally, some implementations can allow you to set the default source addressplaced in all outgoing IP datagrams.

RECEIVE(association id, buffer address, buffer size [,stream id])
-> byte count [,transport address] [,stream id]
[,stream sequence number] [,partial flag] [,payload protocol-id]

Mandatory attributes:

association id:

local handle to the SCTP association.

buffer address:

the memory location indicated by the ULP to store the received message.

buffer size:

the maximum size of data to be received, in bytes.

Optional attributes:

stream id:

to indicate which stream to receive the data on.

stream sequence number:

the Stream Sequence Number assigned by the sending SCTP peer.

partial flag:

if this returned flag is set to 1, then this primitive contains a partialdelivery of the whole message.When this flag is set, the stream id and stream sequence numberaccompanies this primitive.When this flag is set to 0, it indicates that no more deliveries will bereceived for this stream sequence number.

payload protocol-id:

a 32-bit unsigned integer that is received from the peer indicating the typeof payload protocol of the received data.Note that the upper layer is responsible for the host to network byte orderconversion of this field, which is passed by SCTP as 4 bytes of opaquedata.

STATUS(association id) -> status data

• association connection state,
• destination transport address list,
• destination transport address reachability states,
• current receiver window size,
• current congestion window sizes,
• number of unacknowledged DATA chunks,
• number of DATA chunks pending receipt,
• primary path,
• most recent SRTT on primary path,
• RTO on primary path,
• SRTT and RTO on other destination addresses, etc.

Mandatory attributes:

association id:

local handle to the SCTP association.

Optional attributes:

None.

CHANGE HEARTBEAT(association id, destination transport address,
new state [,interval]) -> result

Mandatory attributes:

association id:

local handle to the SCTP association.

destination transport address:

specified as one of the transport addresses of the peer endpoint.

new state:

the new state of heartbeat for this destination transport address(either enabled or disabled).

Optional attributes:

interval:

if present, indicates the frequency of the heartbeat if this is to enableheartbeat on a destination transport address.This value is added to the RTO of the destination transport address.This value, if present, affects all destinations.

REQUESTHEARTBEAT(association id, destination transport address)
-> result

Mandatory attributes:

association id:

local handle to the SCTP association.

destination transport address:

the transport address of the association on which a heartbeat is issued.

Optional attributes:

None.

GETSRTTREPORT(association id, destination transport address)
-> srtt result

Mandatory attributes:

association id:

local handle to the SCTP association.

destination transport address:

the transport address of the association on which the SRTT measurement is tobe reported.

Optional attributes:

None.

SETFAILURETHRESHOLD(association id, destination transport address,
failure threshold) -> result

Mandatory attributes:

association id:

local handle to the SCTP association.

destination transport address:

the transport address of the association on which the failure detectionthreshold is to be set.

failure threshold:

the new value of 'Path.Max.Retrans' for the destination address.

Optional attributes:

None.

SETPROTOCOLPARAMETERS(association id,
[destination transport address,] protocol parameter list)
-> result

Mandatory attributes:

association id:

local handle to the SCTP association.

protocol parameter list:

the specific names and values of the protocol parameters(e.g., 'Association.Max.Retrans' (see Section 16)or other parameters like the DSCP) that the SCTP user wishes to customize.

Optional attributes:

destination transport address:

some of the protocol parameters might be set on a per-destination-transport-address basis.

RECEIVE_UNSENT(data retrieval id, buffer address, buffer size
[,stream id] [, stream sequence number] [,partial flag]
[,payload protocol-id])

Mandatory attributes:

data retrieval id:

the identification passed to the ULP in the SEND FAILURE notification.

buffer address:

the memory location indicated by the ULP to store the received message.

buffer size:

the maximum size of data to be received, in bytes.

Optional attributes:

stream id:

this is a return value that is set to indicate which stream the data wassent to.

stream sequence number:

this value is returned, indicating the Stream Sequence Number that wasassociated with the message.

partial flag:

if this returned flag is set to 1, then this message is a partial delivery ofthe whole message.When this flag is set, the stream id and stream sequence numberaccompanies this primitive.When this flag is set to 0, it indicates that no more deliveries will bereceived for this stream sequence number.

payload protocol-id:

The 32-bit unsigned integer that was set to be sent to the peer, indicatingthe type of payload protocol of the received data.

RECEIVE_UNACKED(data retrieval id, buffer address, buffer size,
[,stream id] [,stream sequence number] [,partial flag]
[,payload protocol-id])

Mandatory attributes:

data retrieval id:

the identification passed to the ULP in the SEND FAILURE notification.

buffer address:

the memory location indicated by the ULP to store the received message.

buffer size:

the maximum size of data to be received, in bytes.

Optional attributes:

stream id:

this is a return value that is set to indicate which stream the data was sentto.

stream sequence number:

this value is returned, indicating the Stream Sequence Number that wasassociated with the message.

partial flag:

if this returned flag is set to 1, then this message is a partial delivery ofthe whole message.When this flag is set, the stream id and stream sequence numberaccompanies this primitive.When this flag is set to 0, it indicates that no more deliveries will bereceived for this stream sequence number.

payload protocol-id:

the 32-bit unsigned integer that was sent to the peer indicating the type ofpayload protocol of the received data.

DESTROY(local SCTP instance name)

Mandatory attributes:

local SCTP instance name:

this is the value that was passed tothe application in the initialize primitive and it indicates whichSCTP instance is to be destroyed.

Optional attributes:

None.

association id:

local handle to the SCTP association.

stream id:

to indicate which stream the data is received on.

association id:

local handle to the SCTP association.

data retrieval id:

an identification used to retrieve unsent and unacknowledged data.

mode:

indicates whether no part of the message never has been sent or if atleast part of it has been sent but it is not completely acknowledged.

cause code:

indicating the reason of the failure, e.g., size toolarge, message life time expiration, etc.

context:

optional information associated with this message(see Section 11.1.5).

association id:

local handle to the SCTP association.

destination transport address:

this indicates the destinationtransport address of the peer endpoint affected by the change.

new-status:

this indicates the new status.

association id:

local handle to the SCTP association.

status:

this indicates what type of event has occurred.

destination transport address list:

the complete set of transport addresses of the peer.

outbound stream count:

the maximum number of streams allowed to be used in this association by the ULP.

inbound stream count:

the number of streams the peer endpoint has requestedwith this association (this might not be the same number as'outbound stream count').

association id:

local handle to the SCTP association.

status:

this indicates what type of event has occurred;the status might indicate that a failure OR a normal termination event occurredin response to a shutdown or abort request.

last-acked:

the TSN last acked by that peer endpoint.

last-sent:

the TSN last sent to that peer endpoint.

Upper Layer Abort Reason:

the abort reason specified in case of auser-initiated abort.

association id:

local handle to the SCTP association.

error info:

this indicates the type of error and optionally some additionalinformation received through the ERROR chunk.

association id:

local handle to the SCTP association.

association id:

local handle to the SCTP association.

• availability of reliable and timely data transport services
• integrity of the user-to-user information carried by SCTP

• avoiding commitment of limited resources before determining that the request for service is legitimate.
• giving priority to completion of processing in progress over the acceptance of new work.
• identification and removal of duplicate or stale queued requests for service.
• not responding to unexpected packets sent to non-unicast addresses.

• by tying up resources at the target SCTP node to which the impersonated node has limited access. For example, the target node can by policy permit a maximum of one SCTP association with the impersonated SCTP node. The masquerading attacker can attempt to establish an association purporting to come from the impersonated node so that the latter cannot do so when it requires it.
• by deliberately allowing the impersonation to be detected, thereby provoking counter-measures that cause the impersonated node to be locked out of the target SCTP node.
• by interfering with an established association by inserting extraneous content such as a SHUTDOWN chunk.

Associations:

A list of current associations and mappings to the data consumers for eachassociation.This might be in the form of a hash table or other implementation-dependentstructure.The data consumers might be process identification information, such as filedescriptors, named pipe pointer, or table pointers dependent on how SCTP isimplemented.

Secret Key:

A secret key used by this endpoint to compute the MAC.This SHOULD be a cryptographic quality random number with a sufficient length.Discussion in [RFC 4086] can be helpful in selection of thekey.

Address List:

The list of IP addresses that this instance has bound.This information is passed to one's peer(s) in INIT and INIT ACK chunks.

SCTP Port:

The local SCTP port number to which the endpoint is bound.

Peer Verification Tag:

Tag value to be sent in every packet and is received in the INIT orINIT ACK chunk.

My Verification Tag:

Tag expected in every inbound packet and sent in the INIT or INIT ACK chunk.

State:

COOKIE-WAIT, COOKIE-ECHOED, ESTABLISHED, SHUTDOWN-PENDING, SHUTDOWN-SENT, SHUTDOWN-RECEIVED, SHUTDOWN-ACK-SENT.

Note: No "CLOSED" state is illustrated, since, if an association is "CLOSED", its TCB SHOULD be removed.

Peer Transport Address List:

A list of SCTP transport addresses to which the peer is bound.This information is derived from the INIT or INIT ACK chunk and is used toassociate an inbound packet with a given association.Normally, this information is hashed or keyed for quick lookup and accessof the TCB.

Primary Path:

This is the current primary destination transport address of the peer endpoint.It might also specify a source transport address on this endpoint.

Overall Error Count:

The overall association error count.

Overall Error Threshold:

The threshold for this association that, if the Overall Error Count reaches, willcause this association to be torn down.

Peer Rwnd:

Current calculated value of the peer's rwnd.

Next TSN:

The next TSN number to be assigned to a new DATA chunk.This is sent in the INIT or INIT ACK chunk to the peer and incremented eachtime a DATA chunk is assigned a TSN (normally, just prior to transmit or duringfragmentation).

Last Rcvd TSN:

This is the last TSN received in sequence.This value is set initially by taking the peer's Initial TSN, received in theINIT or INIT ACK chunk, and subtracting one from it.

Mapping Array:

An array of bits or bytes indicating which out-of-order TSNs have beenreceived (relative to the Last Rcvd TSN).If no gaps exist, i.e., no out-of-order packets have been received, thisarray will be set to all zero.This structure might be in the form of a circular buffer or bit array.

Ack State:

This flag indicates if the next received packet is to be responded to witha SACK chunk.This is initialized to 0.When a packet is received, it is incremented.If this value reaches 2 or more, a SACK chunk is sent and the value is resetto 0.Note: This is used only when no DATA chunks are received out of order.When DATA chunks are out of order, SACK chunks are not delayed(see Section 6).

Inbound Streams:

An array of structures to track the inbound streams, normally including thenext sequence number expected and possibly the stream number.

Outbound Streams:

An array of structures to track the outbound streams, normally including thenext sequence number to be sent on the stream.

Reasm Queue:

A reassembly queue.

Receive Buffer:

A buffer to store received user data that has not been delivered to theupper layer.

Local Transport Address List:

The list of local IP addresses bound in to this association.

Association Maximum DATA Chunk Size:

The smallest Path Maximum DATA Chunk Size of all destination addresses.

Error Count:

The current error count for this destination.

Error Threshold:

Current error threshold for this destination, i.e., what value marks thedestination down if error count reaches this value.

cwnd:

The current congestion window.

ssthresh:

The current ssthresh value.

RTO:

The current retransmission timeout value.

SRTT:

The current smoothed round-trip time.

RTTVAR:

The current RTT variation.

partial bytes acked:

The tracking method for increase of cwnd when in congestion avoidance mode(see Section 7.2.2).

state:

The current state of this destination, i.e., DOWN, UP, ALLOW-HEARTBEAT,NO-HEARTBEAT, etc.

PMTU:

The current known PMTU.

PMDCS:

The current known PMDCS.

Per Destination Timer:

A timer used by each destination.

RTO-Pending:

A flag used to track if one of the DATA chunks sent to this address iscurrently being used to compute an RTT.If this flag is 0, the next DATA chunk sent to this destination is expected tobe used to compute an RTT and this flag is expected to be set.Every time the RTT calculation completes (i.e., the DATA chunk is acknowledged),clear this flag.

last-time:

The time to which this destination was last sent.This can be used to determine if the sending of a HEARTBEAT chunk is needed.

Out Queue:

A queue of outbound DATA chunks.

In Queue:

A queue of inbound DATA chunks.

• through definition of additional chunk types,
• through definition of additional chunk flags,
• through definition of additional parameter types,
• through definition of additional cause codes within ERROR chunks, or
• through definition of additional payload protocol identifiers.

• In the "Chunk Types" registry, IANA has replaced the registry reference to [RFC 4960] and [RFC 6096] with a reference to this document. In addition, in the Notes section, the reference to Section 3.2 of RFC 6096 has been updated with a reference to Section 15.2 of this document. Finally, each reference to [RFC 4960] has been replaced with a reference to this document for the following chunk types:
  • Payload Data (DATA)
  • Initiation (INIT)
  • Initiation Acknowledgement (INIT ACK)
  • Selective Acknowledgement (SACK)
  • Heartbeat Request (HEARTBEAT)
  • Heartbeat Acknowledgement (HEARTBEAT ACK)
  • Abort (ABORT)
  • Shutdown (SHUTDOWN)
  • Shutdown Acknowledgement (SHUTDOWN ACK)
  • Operation Error (ERROR)
  • State Cookie (COOKIE ECHO)
  • Cookie Acknowledgement (COOKIE ACK)
  • Reserved for Explicit Congestion Notification Echo (ECNE)
  • Reserved for Congestion Window Reduced (CWR)
  • Shutdown Complete (SHUTDOWN COMPLETE)
  • Reserved for IETF-defined Chunk Extensions
• In the "Chunk Parameter Types" registry, IANA has replaced the registry reference to [RFC 4960] with a reference to this document. IANA has changed the name of the "Unrecognized Parameters" chunk parameter type to "Unrecognized Parameter" in the "Chunk Parameter Types" registry. In addition, each reference to [RFC 4960] has been replaced with a reference to this document for the following chunk parameter types:
  • Heartbeat Info
  • IPv4 Address
  • IPv6 Address
  • State Cookie
  • Unrecognized Parameter
  • Cookie Preservative
  • Host Name Address
  • Supported Address Types
  IANA has added a reference to this document for the following chunk parameter type:
  • Reserved for ECN Capable (0x8000)
  Also, IANA has added the value 65535 to be reserved for IETF-defined extensions.
• In the "Chunk Flags" registry, IANA replaced the registry reference to [RFC 6096] with a reference to this document. In addition, each reference to [RFC 4960] has been replaced with a reference to this document for the following DATA chunk flags:
  • E bit
  • B bit
  • U bit
  IANA has also replaced the reference to [RFC 7053] with a reference to this document for the following DATA chunk flag:
  • I bit
  IANA has replaced the reference to [RFC 4960] with a reference to this document for the following ABORT chunk flag:
  • T bit
  IANA has replaced the reference to [RFC 4960] with a reference to this document for the following SHUTDOWN COMPLETE chunk flag:
  • T bit
• In the "Error Cause Codes" registry, IANA has replaced the registry reference to [RFC 4960] with a reference to this document. IANA has changed the name of the "User Initiated Abort" error cause to "User-Initiated Abort" and the name of the "Stale Cookie Error" error cause to "Stale Cookie" in the "Error Cause Codes" registry. In addition, each reference to [RFC 4960] has been replaced with a reference to this document for the following cause codes:
  • Invalid Stream Identifier
  • Missing Mandatory Parameter
  • Stale Cookie
  • Out of Resource
  • Unresolvable Address
  • Unrecognized Chunk Type
  • Invalid Mandatory Parameter
  • Unrecognized Parameters
  • No User Data
  • Cookie Received While Shutting Down
  • Restart of an Association with New Addresses
  IANA has also replaced each reference to [RFC 4460] with a reference to this document for the following cause codes:
  • User-Initiated Abort
  • Protocol Violation
• In the "SCTP Payload Protocol Identifiers" registry, IANA has replaced the registry reference to [RFC 4960] with a reference to this document. IANA has replaced the reference to [RFC 4960] with a reference to this document for the following SCTP payload protocol identifier:
  • Reserved by SCTP

• 9 (discard)
• 20 (ftp-data)
• 21 (ftp)
• 22 (ssh)
• 80 (http)
• 179 (bgp)
• 443 (https)

• sctp
• sctp6

• sourceTransportPort
• destinationTransportPort
• collectorTransportPort
• exporterTransportPort
• postNAPTSourceTransportPort
• postNAPTDestinationTransportPort

a)

A long and short name for the new chunk type.

b)

A detailed description of the structure of the chunk, which MUST conform to the basic structure defined in Section 3.2.

c)

A detailed definition and description of intended use of each field within the chunk, including the chunk flags if any. Defined chunk flags will be used as initial entries in the chunk flags table for the new chunk type.

d)

A detailed procedural description of the use of the new chunk type within the operation of the protocol.

a)

A name for the new chunk flag.

b)

A detailed procedural description of the use of the new chunk flag within the operation of the protocol. It MUST be considered that implementations not supporting the flag will send 0 on transmit and just ignore it on receipt.

a)

Name of the parameter type.

b)

Detailed description of the structure of the parameter field. This structure MUST conform to the general Type-Length-Value format described in Section 3.2.1.

c)

Detailed definition of each component of the parameter value.

d)

Detailed description of the intended use of this parameter type and an indication of whether and under what circumstances multiple instances of this parameter type can be found within the same chunk.

e)

Each parameter type MUST be unique across all chunks.

a)

Name of the error condition.

b)

Detailed description of the conditions under which an SCTP endpoint issues an ERROR (or ABORT) chunk with this cause code.

c)

Expected action by the SCTP endpoint that receives an ERROR (or ABORT) chunk containing this cause code.

d)

Detailed description of the structure and content of data fields that accompany this cause code.

• first 2 bytes contain the cause code value
• last 2 bytes contain the length of the error cause.

RTO.Initial:

1 second

RTO.Min:

1 second

RTO.Max:

60 seconds

Max.Burst:

4

RTO.Alpha:

1/8

RTO.Beta:

1/4

Valid.Cookie.Life:

60 seconds

Association.Max.Retrans:

10 attempts

Path.Max.Retrans:

5 attempts (per destination address)

Max.Init.Retransmits:

8 attempts

HB.interval:

30 seconds

HB.Max.Burst:

1

SACK.Delay:

200 milliseconds

[ITU.V42.1994]

International Telecommunications Union, "Error-correcting Procedures for DCEs Using Asynchronous-to-Synchronous Conversion", ITU-T Recommendation V.42, 1994.

[RFC1122]

R. Braden, "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.

[RFC1123]

R. Braden, "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/info/rfc1123>.

[RFC1191]

J.C. Mogul, and S.E. Deering, "Path MTU discovery", RFC 1191, DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.

[RFC1982]

R. Elz, and R. Bush, "Serial Number Arithmetic", RFC 1982, DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.

[RFC2119]

S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC4291]

R. Hinden, and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006,
<https://www.rfc-editor.org/info/rfc4291>.

[RFC4303]

S. Kent, "IP Encapsulating Security Payload (ESP)", RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.

[RFC4895]

M. Tuexen, R. Stewart, P. Lei, and E. Rescorla, "Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)", RFC 4895, DOI 10.17487/RFC4895, August 2007,
<https://www.rfc-editor.org/info/rfc4895>.

[RFC5681]

M. Allman, V. Paxson, and E. Blanton, "TCP Congestion Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
<https://www.rfc-editor.org/info/rfc5681>.

[RFC6335]

M. Cotton, L. Eggert, J. Touch, M. Westerlund, and S. Cheshire, "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry", BCP 165, RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.

[RFC6083]

M. Tuexen, R. Seggelmann, and E. Rescorla, "Datagram Transport Layer Security (DTLS) for Stream Control Transmission Protocol (SCTP)", RFC 6083, DOI 10.17487/RFC6083, January 2011,
<https://www.rfc-editor.org/info/rfc6083>.

[RFC7296]

C. Kaufman, P. Hoffman, Y. Nir, P. Eronen, and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014,
<https://www.rfc-editor.org/info/rfc7296>.

[RFC8126]

M. Cotton, B. Leiba, and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[RFC8174]

B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.

[RFC8200]

S. Deering, and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.

[RFC8201]

J. McCann, S. Deering, J. Mogul, and R. Hinden, "Path MTU Discovery for IP version 6", STD 87, RFC 8201, DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.

[RFC8899]

G. Fairhurst, T. Jones, M. Tüxen, I. Rüngeler, and T. Völker, "Packetization Layer Path MTU Discovery for Datagram Transports", RFC 8899, DOI 10.17487/RFC8899, September 2020,
<https://www.rfc-editor.org/info/rfc8899>.

[FALL96]

K. Fall, and S. Floyd, "Simulation-based Comparisons of Tahoe, Reno, and SACK TCP", July 1996.

[SAVAGE99]

S. Savage, N. Cardwell, D. Wetherall, and T. Anderson, "TCP Congestion Control with a Misbehaving Receiver", October 1999.

[ALLMAN99]

M. Allman, and V. Paxson, "On Estimating End-to-End Network Path Properties", October 1999.

[WILLIAMS93]

R. Williams, "A PAINLESS GUIDE TO CRC ERROR DETECTION ALGORITHMS", August 1993,
<https://archive.org/stream/PainlessCRC/crc_v3.txt>.

[RFC0768]

J. Postel, "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.

[RFC0793]

J. Postel, "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.

[RFC1858]

G. Ziemba, D. Reed, and P. Traina, "Security Considerations for IP Fragment Filtering", RFC 1858, DOI 10.17487/RFC1858, October 1995,
<https://www.rfc-editor.org/info/rfc1858>.

[RFC2104]

H. Krawczyk, M. Bellare, and R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.

[RFC2196]

B. Fraser, "Site Security Handbook", FYI 8, RFC 2196, DOI 10.17487/RFC2196, September 1997,
<https://www.rfc-editor.org/info/rfc2196>.

[RFC2522]

P. Karn, and W. Simpson, "Photuris: Session-Key Management Protocol", RFC 2522, DOI 10.17487/RFC2522, March 1999,
<https://www.rfc-editor.org/info/rfc2522>.

[RFC2960]

R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer, T. Taylor, I. Rytina, M. Kalla, L. Zhang, and V. Paxson, "Stream Control Transmission Protocol", RFC 2960, DOI 10.17487/RFC2960, October 2000,
<https://www.rfc-editor.org/info/rfc2960>.

[RFC3465]

M. Allman, "TCP Congestion Control with Appropriate Byte Counting (ABC)", RFC 3465, DOI 10.17487/RFC3465, February 2003,
<https://www.rfc-editor.org/info/rfc3465>.

[RFC3873]

J. Pastor, and M. Belinchon, "Stream Control Transmission Protocol (SCTP) Management Information Base (MIB)", RFC 3873, DOI 10.17487/RFC3873, September 2004,
<https://www.rfc-editor.org/info/rfc3873>.

[RFC4086]

D. Eastlake 3rd, J. Schiller, and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.

[RFC4301]

S. Kent, and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005,
<https://www.rfc-editor.org/info/rfc4301>.

[RFC4460]

R. Stewart, I. Arias-Rodriguez, K. Poon, A. Caro, and M. Tuexen, "Stream Control Transmission Protocol (SCTP) Specification Errata and Issues", RFC 4460, DOI 10.17487/RFC4460, April 2006,
<https://www.rfc-editor.org/info/rfc4460>.

[RFC4960]

R. Stewart, "Stream Control Transmission Protocol", RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.

[RFC6096]

M. Tuexen, and R. Stewart, "Stream Control Transmission Protocol (SCTP) Chunk Flags Registration", RFC 6096, DOI 10.17487/RFC6096, January 2011,
<https://www.rfc-editor.org/info/rfc6096>.

[RFC6458]

R. Stewart, M. Tuexen, K. Poon, P. Lei, and V. Yasevich, "Sockets API Extensions for the Stream Control Transmission Protocol (SCTP)", RFC 6458, DOI 10.17487/RFC6458, December 2011,
<https://www.rfc-editor.org/info/rfc6458>.

[RFC6951]

M. Tuexen, and R. Stewart, "UDP Encapsulation of Stream Control Transmission Protocol (SCTP) Packets for End-Host to End-Host Communication", RFC 6951, DOI 10.17487/RFC6951, May 2013,
<https://www.rfc-editor.org/info/rfc6951>.

[RFC7053]

M. Tuexen, I. Ruengeler, and R. Stewart, "SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol", RFC 7053, DOI 10.17487/RFC7053, November 2013,
<https://www.rfc-editor.org/info/rfc7053>.

[RFC8260]

R. Stewart, M. Tuexen, S. Loreto, and R. Seggelmann, "Stream Schedulers and User Message Interleaving for the Stream Control Transmission Protocol", RFC 8260, DOI 10.17487/RFC8260, November 2017,
<https://www.rfc-editor.org/info/rfc8260>.

[RFC8261]

M. Tuexen, R. Stewart, R. Jesup, and S. Loreto, "Datagram Transport Layer Security (DTLS) Encapsulation of SCTP Packets", RFC 8261, DOI 10.17487/RFC8261, November 2017,
<https://www.rfc-editor.org/info/rfc8261>.

[RFC8540]

R. Stewart, M. Tuexen, and M. Proshin, "Stream Control Transmission Protocol: Errata and Issues in RFC 4960", RFC 8540, DOI 10.17487/RFC8540, February 2019,
<https://www.rfc-editor.org/info/rfc8540>.

• CRC input data is assigned to a byte stream, numbered from 0 to N-1.
• The transport-level byte stream is mapped to a polynomial value. An N-byte PDU with j bytes numbered 0 to N-1 is considered as coefficients of a polynomial M(x) of order 8*N-1, with bit 0 of byte j being coefficient x^8*(N-j)-8 and bit 7 of byte j being coefficient x^8*(N-j)-1.
• The CRC remainder register is initialized with all 1s and the CRC is computed with an algorithm that simultaneously multiplies by x³² and divides by the CRC polynomial.
• The polynomial is multiplied by x³² and divided by G(x), the generator polynomial, producing a remainder R(x) of degree less than or equal to 31.
• The coefficients of R(x) are considered a 32-bit sequence.
• The bit sequence is complemented. The result is the CRC polynomial.
• The CRC polynomial is mapped back into SCTP transport-level bytes. The coefficient of x³¹ gives the value of bit 7 of SCTP byte 0, and the coefficient of x²⁴ gives the value of bit 0 of byte 0. The coefficient of x⁷ gives bit 7 of byte 3, and the coefficient of x⁰ gives bit 0 of byte 3. The resulting 4-byte transport-level sequence is the 32-bit SCTP checksum value.

<CODE BEGINS>
/****************************************************************/
/* Note: The definitions for Ross Williams's table generator    */
/* would be TB_WIDTH=4, TB_POLY=0x1EDC6F41, TB_REVER=TRUE.      */
/* For Mr. Williams's direct calculation code, use the settings */
/* cm_width=32, cm_poly=0x1EDC6F41, cm_init=0xFFFFFFFF,         */
/* cm_refin=TRUE, cm_refot=TRUE, cm_xorot=0x00000000.           */
/****************************************************************/

/* Example of the crc table file */
#ifndef __crc32cr_h__
#define __crc32cr_h__

#define CRC32C_POLY 0x1EDC6F41UL
#define CRC32C(c,d) (c=(c>>8)^crc_c[(c^(d))&0xFF])

uint32_t crc_c[256] = {
  0x00000000UL, 0xF26B8303UL, 0xE13B70F7UL, 0x1350F3F4UL,
  0xC79A971FUL, 0x35F1141CUL, 0x26A1E7E8UL, 0xD4CA64EBUL,
  0x8AD958CFUL, 0x78B2DBCCUL, 0x6BE22838UL, 0x9989AB3BUL,
  0x4D43CFD0UL, 0xBF284CD3UL, 0xAC78BF27UL, 0x5E133C24UL,
  0x105EC76FUL, 0xE235446CUL, 0xF165B798UL, 0x030E349BUL,
  0xD7C45070UL, 0x25AFD373UL, 0x36FF2087UL, 0xC494A384UL,
  0x9A879FA0UL, 0x68EC1CA3UL, 0x7BBCEF57UL, 0x89D76C54UL,
  0x5D1D08BFUL, 0xAF768BBCUL, 0xBC267848UL, 0x4E4DFB4BUL,
  0x20BD8EDEUL, 0xD2D60DDDUL, 0xC186FE29UL, 0x33ED7D2AUL,
  0xE72719C1UL, 0x154C9AC2UL, 0x061C6936UL, 0xF477EA35UL,
  0xAA64D611UL, 0x580F5512UL, 0x4B5FA6E6UL, 0xB93425E5UL,
  0x6DFE410EUL, 0x9F95C20DUL, 0x8CC531F9UL, 0x7EAEB2FAUL,
  0x30E349B1UL, 0xC288CAB2UL, 0xD1D83946UL, 0x23B3BA45UL,
  0xF779DEAEUL, 0x05125DADUL, 0x1642AE59UL, 0xE4292D5AUL,
  0xBA3A117EUL, 0x4851927DUL, 0x5B016189UL, 0xA96AE28AUL,
  0x7DA08661UL, 0x8FCB0562UL, 0x9C9BF696UL, 0x6EF07595UL,
  0x417B1DBCUL, 0xB3109EBFUL, 0xA0406D4BUL, 0x522BEE48UL,
  0x86E18AA3UL, 0x748A09A0UL, 0x67DAFA54UL, 0x95B17957UL,
  0xCBA24573UL, 0x39C9C670UL, 0x2A993584UL, 0xD8F2B687UL,
  0x0C38D26CUL, 0xFE53516FUL, 0xED03A29BUL, 0x1F682198UL,
  0x5125DAD3UL, 0xA34E59D0UL, 0xB01EAA24UL, 0x42752927UL,
  0x96BF4DCCUL, 0x64D4CECFUL, 0x77843D3BUL, 0x85EFBE38UL,
  0xDBFC821CUL, 0x2997011FUL, 0x3AC7F2EBUL, 0xC8AC71E8UL,
  0x1C661503UL, 0xEE0D9600UL, 0xFD5D65F4UL, 0x0F36E6F7UL,
  0x61C69362UL, 0x93AD1061UL, 0x80FDE395UL, 0x72966096UL,
  0xA65C047DUL, 0x5437877EUL, 0x4767748AUL, 0xB50CF789UL,
  0xEB1FCBADUL, 0x197448AEUL, 0x0A24BB5AUL, 0xF84F3859UL,
  0x2C855CB2UL, 0xDEEEDFB1UL, 0xCDBE2C45UL, 0x3FD5AF46UL,
  0x7198540DUL, 0x83F3D70EUL, 0x90A324FAUL, 0x62C8A7F9UL,
  0xB602C312UL, 0x44694011UL, 0x5739B3E5UL, 0xA55230E6UL,
  0xFB410CC2UL, 0x092A8FC1UL, 0x1A7A7C35UL, 0xE811FF36UL,
  0x3CDB9BDDUL, 0xCEB018DEUL, 0xDDE0EB2AUL, 0x2F8B6829UL,
  0x82F63B78UL, 0x709DB87BUL, 0x63CD4B8FUL, 0x91A6C88CUL,
  0x456CAC67UL, 0xB7072F64UL, 0xA457DC90UL, 0x563C5F93UL,
  0x082F63B7UL, 0xFA44E0B4UL, 0xE9141340UL, 0x1B7F9043UL,
  0xCFB5F4A8UL, 0x3DDE77ABUL, 0x2E8E845FUL, 0xDCE5075CUL,
  0x92A8FC17UL, 0x60C37F14UL, 0x73938CE0UL, 0x81F80FE3UL,
  0x55326B08UL, 0xA759E80BUL, 0xB4091BFFUL, 0x466298FCUL,
  0x1871A4D8UL, 0xEA1A27DBUL, 0xF94AD42FUL, 0x0B21572CUL,
  0xDFEB33C7UL, 0x2D80B0C4UL, 0x3ED04330UL, 0xCCBBC033UL,
  0xA24BB5A6UL, 0x502036A5UL, 0x4370C551UL, 0xB11B4652UL,
  0x65D122B9UL, 0x97BAA1BAUL, 0x84EA524EUL, 0x7681D14DUL,
  0x2892ED69UL, 0xDAF96E6AUL, 0xC9A99D9EUL, 0x3BC21E9DUL,
  0xEF087A76UL, 0x1D63F975UL, 0x0E330A81UL, 0xFC588982UL,
  0xB21572C9UL, 0x407EF1CAUL, 0x532E023EUL, 0xA145813DUL,
  0x758FE5D6UL, 0x87E466D5UL, 0x94B49521UL, 0x66DF1622UL,
  0x38CC2A06UL, 0xCAA7A905UL, 0xD9F75AF1UL, 0x2B9CD9F2UL,
  0xFF56BD19UL, 0x0D3D3E1AUL, 0x1E6DCDEEUL, 0xEC064EEDUL,
  0xC38D26C4UL, 0x31E6A5C7UL, 0x22B65633UL, 0xD0DDD530UL,
  0x0417B1DBUL, 0xF67C32D8UL, 0xE52CC12CUL, 0x1747422FUL,
  0x49547E0BUL, 0xBB3FFD08UL, 0xA86F0EFCUL, 0x5A048DFFUL,
  0x8ECEE914UL, 0x7CA56A17UL, 0x6FF599E3UL, 0x9D9E1AE0UL,
  0xD3D3E1ABUL, 0x21B862A8UL, 0x32E8915CUL, 0xC083125FUL,
  0x144976B4UL, 0xE622F5B7UL, 0xF5720643UL, 0x07198540UL,
  0x590AB964UL, 0xAB613A67UL, 0xB831C993UL, 0x4A5A4A90UL,
  0x9E902E7BUL, 0x6CFBAD78UL, 0x7FAB5E8CUL, 0x8DC0DD8FUL,
  0xE330A81AUL, 0x115B2B19UL, 0x020BD8EDUL, 0xF0605BEEUL,
  0x24AA3F05UL, 0xD6C1BC06UL, 0xC5914FF2UL, 0x37FACCF1UL,
  0x69E9F0D5UL, 0x9B8273D6UL, 0x88D28022UL, 0x7AB90321UL,
  0xAE7367CAUL, 0x5C18E4C9UL, 0x4F48173DUL, 0xBD23943EUL,
  0xF36E6F75UL, 0x0105EC76UL, 0x12551F82UL, 0xE03E9C81UL,
  0x34F4F86AUL, 0xC69F7B69UL, 0xD5CF889DUL, 0x27A40B9EUL,
  0x79B737BAUL, 0x8BDCB4B9UL, 0x988C474DUL, 0x6AE7C44EUL,
  0xBE2DA0A5UL, 0x4C4623A6UL, 0x5F16D052UL, 0xAD7D5351UL,
};

#endif


/* Example of table build routine */

#include <stdio.h>
#include <stdlib.h>

#define OUTPUT_FILE   "crc32cr.h"
#define CRC32C_POLY    0x1EDC6F41UL

static FILE *tf;

static uint32_t
reflect_32(uint32_t b)
{
  int i;
  uint32_t rw = 0UL;

  for (i = 0; i < 32; i++) {
    if (b & 1)
      rw |= 1UL << (31 - i);
    b >>= 1;
  }
  return (rw);
}

static uint32_t
build_crc_table (int index)
{
  int i;
  uint32_t rb;

  rb = reflect_32(index);

  for (i = 0; i < 8; i++) {
    if (rb & 0x80000000UL)
      rb = (rb << 1) ^ (uint32_t)CRC32C_POLY;
    else
      rb <<= 1;
  }
  return (reflect_32(rb));
}

int
main (void)
{
  int i;

  printf("\nGenerating CRC32c table file <%s>.\n",
  OUTPUT_FILE);
  if ((tf = fopen(OUTPUT_FILE, "w")) == NULL) {
    printf("Unable to open %s.\n", OUTPUT_FILE);
    exit (1);
  }
  fprintf(tf, "#ifndef __crc32cr_h__\n");
  fprintf(tf, "#define __crc32cr_h__\n\n");
  fprintf(tf, "#define CRC32C_POLY 0x%08XUL\n",
    (uint32_t)CRC32C_POLY);
  fprintf(tf,
    "#define CRC32C(c,d) (c=(c>>8)^crc_c[(c^(d))&0xFF])\n");
  fprintf(tf, "\nuint32_t crc_c[256] =\n{\n");
  for (i = 0; i < 256; i++) {
    fprintf(tf, "0x%08XUL,", build_crc_table (i));
    if ((i & 3) == 3)
      fprintf(tf, "\n");
    else
      fprintf(tf, " ");
  }
  fprintf(tf, "};\n\n#endif\n");

  if (fclose(tf) != 0)
    printf("Unable to close <%s>.\n", OUTPUT_FILE);
  else
    printf("\nThe CRC32c table has been written to <%s>.\n",
      OUTPUT_FILE);
  return (0);
}

/* Example of crc insertion */

#include "crc32cr.h"

uint32_t
generate_crc32c(unsigned char *buffer, unsigned int length)
{
  unsigned int i;
  uint32_t crc32 = 0xffffffffUL;
  uint32_t result;
  uint32_t byte0, byte1, byte2, byte3;

  for (i = 0; i < length; i++) {
    CRC32C(crc32, buffer[i]);
  }

  result = ~crc32;

  /*  result now holds the negated polynomial remainder,
   *  since the table and algorithm are "reflected" [williams95].
   *  That is, result has the same value as if we mapped the message
   *  to a polynomial, computed the host-bit-order polynomial
   *  remainder, performed final negation, and then did an
   *  end-for-end bit-reversal.
   *  Note that a 32-bit bit-reversal is identical to four in-place
   *  8-bit bit-reversals followed by an end-for-end byteswap.
   *  In other words, the bits of each byte are in the right order,
   *  but the bytes have been byteswapped.  So, we now do an explicit
   *  byteswap.  On a little-endian machine, this byteswap and
   *  the final ntohl cancel out and could be elided.
   */

  byte0 = result & 0xff;
  byte1 = (result>>8) & 0xff;
  byte2 = (result>>16) & 0xff;
  byte3 = (result>>24) & 0xff;
  crc32 = ((byte0 << 24) |
           (byte1 << 16) |
           (byte2 << 8)  |
           byte3);
  return (crc32);
}

int
insert_crc32(unsigned char *buffer, unsigned int length)
{
  SCTP_message *message;
  uint32_t crc32;

  message = (SCTP_message *)buffer;
  message->common_header.checksum = 0UL;
  crc32 = generate_crc32c(buffer,length);
  /* and insert it into the message */
  message->common_header.checksum = htonl(crc32);
  return (1);
}

int
validate_crc32(unsigned char *buffer, unsigned int length)
{
  SCTP_message *message;
  unsigned int i;
  uint32_t original_crc32;
  uint32_t crc32;

  /* save and zero checksum */
  message = (SCTP_message *)buffer;
  original_crc32 = ntohl(message->common_header.checksum);
  message->common_header.checksum = 0L;
  crc32 = generate_crc32c(buffer, length);
  return ((original_crc32 == crc32) ? 1 : -1);
}
<CODE ENDS>

Randall R. Stewart

Michael Tüxen

Karen E. E. Nielsen